I see two problems with Sakura's character/story and why people didn't like her.
First, her story never gets finished. She has as good arc and is an active part of Team 7, all the way up through the 'thank you' hug scene in Shippuden. But after that, her story completely flatlines. There is no more growth, no more challenge. Her confession? Just a plot device to move Naruto along after Sasuke. It changed nothing for either Naruto or Sakura. Kishimoto leaves Sakura with all the desperation and bad decisions and scuttled confession, and never writes her learning from it, or there being a positive outcome. Sakura is never shown turning Naruto's head. He still is as focused on Sasuke as ever, until the very end. Sakura's story is never finished.
Second, Sakura will forever be unfairly compared to Hinata. Not compared to the best version of what her own character could have been, as the single heroine and love interest of the story. Though it didn't start out this way, by the end, Sakura's character is placed in stark comparison to Hinata's character, over and over and over again. And there is literally not enough about Hinata to even dislike. Hinata's whole sick focus is on Naruto. And she is rewarded for that. Kishimoto draws her in flattering, wide-eyed poses, and she is constanly shown as fearful/worried and needing to be saved. Even her brief flashes of bravery are tied to Naruto somehow. She is shown as the damsel in distress, and she is given pretty speeches about how great Naruto is when she is saved. Every friggin time. Sakura gets none of this treatment. Even though she is braver, more heroic, more kind-hearted and would literally die to save Naruto (not trip over a rock).
I don't think the problem is with Sakura. If you took Hinata out of the story (which literally wouldn't change the story a bit), then there is no one else for Sakura to be compared to. And her efforts would shine out like they should. But instead, Kishimoto put a big red arrow flashing "love interest" over Hinata and gave her sappy lines only adoring Naruto over everything and everyone else (including her dead cousin), and people fell for it.
Indeed, She lacked a resolution to her character despite being hyped up to drive the story as much as her teammates, and fell flat at the end because no one can interfere with Naruto and Sasuke's destined clash. But I don't think that is why haters hate her, because you don't see the complaints being about that. It is all "Sakura is a kitten." "She is mean and abusive to Naruto" "She doesn't deserve Naruto." "Just have that sexy, stone cold Bastard Boyfriend Sasuke Uchiha smack some sense into you and make way for the OTP Naruto Uzumaki and Hinata Hyuga". None of the complaints I have ever heard in my life about Sakura Haruno from her haters and Hinata fanatics has ever been about what she lacks as a character. It has always been that she is shipping material and just because she was among the many many villagers that did not show Naruto any affection as a kid she is demonized. But what makes it especially unforgivable in her haters eyes, is that she was the object of Naruto's affections. That apparently is the double standard here when I think about it, because I don't see even the nameless villagers that gave him cold heartless gazes and pull their children away from him getting a fraction of the hate Sakura was getting. Nor were any of Sasuke's other fan girls, including Ino were raged at for crushing on him for being a bad boy, instead of the poor socially and emotionally abused orphan Naruto Uzumaki. And again here is another double standard too ,they accuse Sakura not being of any comfort to Naruto and just stood back and watched him be ostracized, but Hinata did the same since according to the story the two were never acquainted in childhood either. But despite that, Sakura is the only one that gets bashed for it.
And ultimately I and some others here have had this pointed out many many times. Sakura had grown exponentially as a character from the early to mid stages of the time skip a.k.a. Shippuden that you could swear that you were not even looking same character anymore. But will any of her haters acknowledge that character development? NOPE 
So you see, it doesn't really matter how well developed Sakura's character is or even if her character arc concluded properly she will always be a character hated more than the most unsympathetic, vile villains in the story because she is supposed to be Naruto's love interest but she is nothing but a "ball buster" to him and drools over the "cool mysterious bad boy" which again all of this grudge is stemming form Naruto's abused and tragic childhood.
Your second point, sadly, is the prime, de facto argument all of Sakura's haters will ever use to try win these debates. Sakura is not Hinata. Sakura will never be as good as Hinata. Sakura is not worthy of standing in the same presence as Hinata. Why is this? Again Hinata was the one crushing one the sad lonely little orphan when no one else did. Especially Sakura, whom again did not, despite Naruto having a crush on her and has shown time and time again genuine love for her. That is why these Hinata cultists are so enamored with her. I don't think I need to say more because this, I am sure is the only reason Hinata is loved the way she is and Sakura is always compared to her in a negative way. And as you have said before Tricksie, all of those that empathize with Naruto never having his crush look his way and instead squealling over the "bad boy" want sweet, vicarious, emotional revenge by imagining Naruto getting hitched with Hinata and if Sakura wants him afterwards he will say to her " GET LOST, you're not worth it anymore!!! I have found an even better woman!!!" 
Anyways that is how I view things, and judging by how these fanatics argue things I don't think I'm wrong. You are of course very right, but that is not how these haters view it I think, because they never have and never will complain about how Sakura lacks development. They just viciously tear into her for not, being worthy of Naruto's affections because of her initial treatment of him. Yet ironically, every time Hinata is on panel or screen it is SUCH A HUGE STEP IN DEVELOPING HER to be Naruto perfect trophy wife. 
Edited by Phantom_999, 17 February 2020 - 02:00 AM.
Damn, girl, talk about being on point!! 
And I feel too that that really is a shame Sakura is always like that.
