The thing is that Sakura and Hinata are two different characters. Sakura being a main character and Hinata being a side character is a single fact that is enough to tell us for how they should be as characters and how they would roll in a manga.
Sakura has many aspects and roles that concerns the plot, other characters, special cases like being Tsunade's desciple, etc. While Hinata almost everything should revolve about something in particular and the rest is bits here and there like any other side character.
You can say it's the principles and basis of manga on how they are and should be.
The main issue with Sakura and Hinata is 2 fold on kishi's part, he missed opportunities to make Sakura better than he did and for Hinata he could have just expanded the story. Though there is fault for his missed time on Sakura, he missed a lot more with Hinata. I'll explain:
Sakura: As the heroine, kishi has used Sakura but the degree he could have used her could have been better. Sakura did have increments of growth in part 1 and he did make good on her development in the start of part 2. Sakura was able to display her abilities and she got a major fight. However in the time she has spent onscreen, it became apparent that Sakura is a mentally driven character predominant while her physical development is secondary. Basically there were times when he could have given Sakura more attention, kinda like the early parts of part 2, with the kazekage rescue and sasuke and sai arcs. There was plenty of situations in which he could have given Sakura some physical driven development beyond Sasori. A fight between her and Kabuto would have been great back in the Sasuke and Sai arc. Another chance was for her own training back in the time Naruto was learning wind style. One of the biggest opportunities was also in the war for her to face Chiyo if it came to that. Sakura has had some great moments beyond Sasori, that is true I mean nailing the centipede in the pain arc, busting the white zetsu, and now demolishing a horde of jubbi spawn and both summoning katsuyu and healing people, she has had good moments but if anything Sakura's predominant traits for her development are mentally driven, basically her actions tend to flow with the story, this is apparent from major events like Sasuke getting the curse mark, Naruto saving her from Gaara, Sasuke running away, Naruto making the promise, her getting stronger for her team 7, the burdens and curses both her teammates faced, Sasuke's actions, the land of iron, resolving to help Naruto in the fight against obito. More or less her mental development and outlook towards the effects and actions on/caused too others, mainly team 7, is what her character is about. This is also a bit logical in a sense as Sakura was created to be the human element of team 7, this includes human weakness and emotional events. As in what was she the normal girl with no losses or inherited powers to do in a team where her 2 teammates had suffered loss and loneliness? There were times kishi could have done more with Sakura to give her more time kinda like he gave Naruto screentime for 3 training sessions while Sasuke was just given the myangeko on the fly during other fights and Sakura's herself occurred as a work in progress from the timeskip. But overall she has not been bad in other means. Heroes and Heroines do not need to be all powerhouses and able to wreak mountains, I mean now Sakura is able to shake the earth greatly and patch up many people at once, but she has been good where it counts, fulfilling the humanity she was made to represent. If it were not for anime or fillers, she would have not had some extended scenes for fighting which is at least a benefit in some aspects here (this can apply to any and all characters kinda like Asuma in the sora arc before he was axed off he really only had a small scuffle with the sound nin before they tried to kill Shikamaru and had a short encounter with Kisame, his only real fights were against Hidan who he dies against and against his own team as en edo tensei zombie but that had story purpose too.) Even then Sakura is I would say as a character who has developed over the story is 80% mentally built, 20% physically built, this is due to her events in the manga, but she still has her moments where it counts in both of them. She is definitely a mentally driven heroine but still has her own physical aspects that make her notable. Also as a side note, yes many felt her powerup was a quick random occurrence, it was not, it had a purpose, the Sannin deadlock. No matter how strong or weak Tsunade seemed to ororchimaru or Jiraya, they all had their ups and downs on each other, Kishi confirms this. I mean we see Tsunade the most in the series out of any Sannin. Sakura is able to use kage level power now, not as much as Naruto or Sasuke, but she still has her purpose to be a force of her own, this includes healing knowledge as a medical ninja. Her powerup serves a purpose, to keep that Sannin deadlock theme alive. But in all, Sakura is a good character, a mentally driven heroine who you see growing up as the story moves on, she moves from being a pure daydreaming child with no talents to a serious and committed ninja who gains respect for others and others gain respect for her peers over her mastery of medical and chakra enhanced strength.
Hinata: Hinata as a character, while the backstory is easily understood and the plot was able to be expanded. It never was. In the same way Kishi missed opportunities of physical growth for Sakura, There were cases where he missed Hinata entirely. The deal with Hinatas growth compared to Sakura's is, its limited. Hers is very very limited. There have been cases when Sakura has been sidelined but for Hinata, those times of being sidelined are even greater. Remember the time Sakura was basically sidelined during the Return of Itachi and search for Tsunade arc? She came back in the following when Sasuke defected, this brought forth the important promise of a lifetime scene and gave her growth in which she saw Naruto as a full friend. Hinata though, her time of importance was in the chunin exams and the moment Naruto finished pummeling Neji, that importance would end until she made another scene in the pain arc. As a side character yes Hinata is naturally not going to be expected to have as much as screentime as Sakura, the problem here though is, whenever Sakura was missing or out of the picture, it was like 3X the length for Hinata. Even then there are other side characters who have had much more important reoccuring roles that notably impact or influence others like Naruto or others significantly more then her. Characters like Shikamaru, Tsunade, Gaara, even Bee and Nagato have had more impact on Naruto than Hinata and they appear even less. Bee spent a whole lot of time with Naruto which was important in how they could relate and also how they had the same ideals for those they cared about. Nagato even, for his one fight with Naruto and then minor sealing upon re meeting, you find that Naruto focuses on Nagato more than Hinata during the events between her defense and Nagato's story. The problem with Hinata is she had the set-up for a story which could have been expanded, could have grown into something more but she became less important in the long run. Hinata's only real correlation characters were Naruto and Neji. Shino and Kiba were her teammates but their development likewise is limited, yet you still see Kiba at least getting a fair amount of attention even for a guy with just 1 battle. The story of the Hyuga was present and open for expansion but this storyline basically ended when the Sage of the 6 paths was introduced. The Byuakgun no longer had a place of central importance in the storyline as it once could have. Neji appeared more than Hinata herself as well, his story was given a good driven path of former foe to good friend. But in terms of lasting roles, Hinata misses about 300 or so chapters of importance between the time the chunin exam fight again neji ends and until her event in the pain arc. Even then that involvement just gets nearly forced to the back. We don't see any mention or reflection of it for a long time, only a short memory from when Naruto's clone saved her. Then we get 615 but again, its quickly bypassed this time only Hinata remembering the event. I'm not speaking out of pairings here, just that with her total involvement, it is so limited its like at this point we see Hinata do something major then she just tends to only be present and stand around like the other majority cast. The main deal here is Hinata has less screentime, less screentime=less we can work with her. She is not as complex as others. If Hinata had at least the presence of Shikamaru, or team 8 itself was given more time, maybe if they got their own arc like team 10 did then it would make more sense to call Hinata a major character but she is not, she is a minor character. When Neji died, her own involvement in the plot became much more restricted. Aside from Naruto there is not much else who she correlates with. When the time comes for Sasuke to be dealt with this is her biggest downfall, she never even said a word to the guy (save in the bonds movie). Now she is just being a watcher for Sakura to keep updated on the battlefield. Hinata has a bit left in her but to call her completely important would be an understatement, she has her moments but if Kishi does not build on those then where does her development go? Where does it lead? Sakura's speech from 630 was in part because of her experience in the land of iron, even in 635 that has been built upon too from the land of iron and 540. So what is Hinata's development to be if her own moments are all but placed in the background? This is the problem with Hinata, she is too limited but as the story is now its too late, her major moment so far was 615 but if Kishi didn't build on that, if Naruto still loves Sakura, if he even gave us a hint of NS from 631 using Minato no less then whats the point of her romantic hopes of Naruto? This is the problem with Hinata, she is too limited making her a grey character. The manga is almost done, the major fights are coming, Naruto vs Sasuke is a team 7 only zone, not team 7 plus Hinata. Aside from gaining confidence and approval to lead her clan and stand beside Naruto as an acknowledged ally, I cannot see much else for her espcially when her own development from 633 feels kinda like a reversion/repeat of the stuff we know she has said for years and still has not gone much of anywhere. In fact this is where I see in part why NH is not able to work, because when Kishi is showing us the hints of NS and Naruto still loving Sakura this late, and still nothing on Hinata's end what are we to expect? Sakura cannot go over to Sasuke or it would uproot her development and just make her growth become unwarranted. It would make Naruto's promise to her unimportant, even then thats it, the promise and the development around Naruto, we see this brought up more times than Hinata even appears and we are to somehow expect Naruto to just foresake what he said to Sakura? No. just no. Hinata is a decent character but as the manga was written and we see the majority of the stuff laid out focusing mostly on NS, there cannot be a sudden shift or turn in which Hinata gets a free and convenient open pass for Naruto to like her, espcially when we see the development his love for Sakura and her concern and care for him has taken, espcially now with development showing Naruto still loves Sakura, Minato sees her like Kushina, Kushina gave a foreshadow of Naruto wanting a girlfriend like her, and Sakura starting to not trust Sasuke. Hinata's own limitation is in effect the hindrance to NH. If she was around more it would be bigger but she was not. Hinata is decent, but because she has limited attention, this makes her not as developed and in effect easier to understand because there is less content with her.
like thatll ever happen, but those were only like 3 comments. The rest were like how shes awesome and cute and perfect and how sakira is the best heroine. Hinata doesnt get that kind of attention and its only natural, I mean, shes not in the top ten popular charscters amongst the japanese shes not that popular. Sakura is the heroine and shes the top female. What do you expect? Shes loved amongst the japanese. I resd the japanese comments and they said? "Wow sakura-chan is so pretty!" Or "this is so cute" and "your perfect as sakura" and "great cosplay as the heroine" and "wow awesome cosplay" and sasaki replied back to them like, "yes thank you thats great!" Nigahiga liked the video and thanked her for her help. Some other japanese youtubers replied "it was really fun! We shoukd do this more often!" Basically, the japanese fans were all "wows" and "great" and "happy" and all about how sakura looks great and cute and how sasaki looks great. Only natural response! 
). If you don't see her in action, people call her useless even though she's spending her energy and chakra healing people. If she does jump into action and displays what she is really capable of, people will call it an asspull or will look for any excuse necessary to completely downgrade her performance. I don't get what the western fans want from Sakura. My best guess is that they want her to disappear from the series, but unfortunately for them, that's not going to happen anytime soon ;).
