Its not really that kishi made too many characters, some have been given more prominence than others if we count out team 7. I mean if we look at all the leaf characters you will see the hiearchy of importance out of the K11.
Most important/mains: Naruto, Sakura, Sasuke, reason? Hero, Heroine, and anti-hero/temp antagonist. Obviously they get the main focus no question.
Major focus: Shikmaru mostly, a couple fights, majorly centered during Asuma's death, grew to his role in the 4th shinobi war. Sai follows this, he is a major character, learning about the need for bonds or rather sai is becoming more human with his own emotions. Finally Neji, Neji has been given more forefront development on his team than any other. A few fights to a death, his changed perspective makes him much more of a major character than his cousin.
Moderate focus: These guys are seen every now and then, they have fair amounts of time.
Ino and Choji- mainly tied to what Shikamaru does but they have their own moments too. Ino had her time in the Hidan and Kakuzu arc along with her father's death. Choji had his own fight against one of the sound 4 and grew mentally better over what everyone told him. Generally they are both in and out but corrlate with Shikamaru due to the Ino-Shika-Cho stuff.
Kiba and Akamaru- Out of team 8, Kiba is the most unique cause well, he has Akamaru tagging along the whole time. He isn't needed to be tied to anything major, he has a way of doing his own short things even if just comic outbursts. He was fairly used, having his own fight with Naruto, the sound 4, and a couple other minor events.
Lee- Lee has his own story of the ninja who cannot use ninjutsu. He kinda fluxs in and out of importance. He was prominent around the chunin exams, vs Kimimaro, and during the kazekage rescue arc. Had a major event with Neji's death being at the forefront of the assault with Naruto. Though a potential character, kishi has left him just self stable despite the limited usage.
Minor: These are characters who hardly pop up, generally very limited
Hinata: Yes Hinata is in here, despite 2 major moments, she has 2 high moments but not enough consistent development, aka simple screentime or simple development which can simply just be stuff like talking during downtimes or we see something else from her. Hardest part of all, her character is dependent on Naruto and Neji, just because she loves Naruto, this is also what kinda limits her character. Kishi had a lot of more story potential he could have used for her, but with Neji gone, the only thing keeping her tied to the story is Naruto, unless he decides to put the Hyuga inhertiance back up for Hinata to lead, maybe things can work then. But its just too far too late, she hasn't had a major importance in the gap between the end of Neji's fight with Naruto and her moment against pain. Thats over 300 chapters of nothing! This is a reason why Hinata is minor, 2 major events makes her a bit higher than Kiba in terms of importance like she can be the most prominant member of team 8 shown, but when it all averages out, the 2 moments she has cannot coverup all the stuff she has missed or doesn't have. Hinata is basically developed more in fillers and in importance to the manga, she may be more of a token love interest character if nothing else.
Shino: Shino is an enigma, he has practically no fights on screen in the manga save against Orochimaru's henchman Zaku. He is rather a mob type character, always with a crowd. He has some minor remarks and he has skills, the databook makes this clear. Shino is cool and has a unique power, but he is just unaddressed. He has a few fillers to show, technically he does have a canon fight with kankuro, just offscreen but the filler in the anime shows this so its okay to a degree. Shino is good but not used.
Tenten: basically the most cyrptic and unknown character of all. She has fights in the manga, but offscreen. They are addressed in fillers. Tenten is just there to be there, nothing else. You can miss her without impacting the story. She did get to use the sage's fan but there's basically nothing else.
In the end kishi did give a different amount of focus to each character, but this was better than Oda's in onepiece where every character needs long amounts of screentime just to get a point of development. Kishi put in a lot but didn't focus on them all equally.
The bolded: I can not begin to tell you how much I disagree with that statement. I truly don't get how anyone can look at the massive list of characters and the limited focus given to only a handful of them and say the size of the cast is not an issue. Let's look at Sakura as an example, I love and adore her but there are some people like Cudos N and others who feel she is not treated the way a heroine should be, and while I may not entirely share their views on the subject, I understand their concerns and gripes and I don't feel they are totally invalidated in feeling that way. If there are readers looking at the heroine this way, something is wrong.
Kishimoto's focus on his characters is hugely uneven, another example of this is Bee. He is basically just a replacement for Jiraiya as Naruto's mentor, he served that role and now what is he doing? Absolutely nothing significant. It makes zero sense, seeing as he is the only other jinchuuriki on the battlefield, and logically he should be assisting directly in the fight against Obito. But, in order for Kishi to drill home his message of the "new generation surpassing the old", Bee has become unimportant.
I also find it quite amusing that you actually placed Kiba and Akamaru's importance above Hinata. I may find her uninteresting, but this arc proves that she does have sizable relevance, otherwise, I don't think 615 would have happened. She is the embodiment of Naruto's influence on others and his inherent ability to change and encourage people. No matter how you try to slice it, she can no longer be relegated to 'minor character' status. A minor character would be Karui or Omoi.
A character's importance is NOT defined by the number of times they show up in the story, their significance is measured in the overall affect they have on the plot and other characters.