Izuku Stagnated As A Character, Reaching A Point In His Development And Never Growing Beyond It. Throughout

Izuku stagnated as a character, reaching a point in his development and never growing beyond it. Throughout BNHA, he learned about how unfair and corrupt Hero Society was, even being a victim of it himself when he was quirkless. 

Izuku would experience doubt and start to question the world he idolized for so long, only to return to worshiping and defending it. He kept speaking about “saving” Tomura but failed and acted as if he couldn’t because heroes can’t “save” everyone. In the end, Izuku and his classmates become cogs in Hero Society’s machine, and nothing changes. He repeatedly encountered proof of Hero Society’s failure, but in the end, none of this mattered to him.

Instead of becoming the catalyst of change and leading it with his classmates and the League of Villains, Izuku decided to accept Hero Society as is. He's so blinded by his adoration for heroes that he ignores the corruption and flaws of the society they uphold. 

Horikoshi hit a wall with Izuku’s character, reducing him to a pro-Hero Society bootlicker instead of making him someone who is a hero of change and improvement.