I think you misinterpreted the point of Deku's character. His goal was never to become the No.1 hero, it was to become the world's greatest hero, which he absolutely succeeded in. He was the only person capable of taking out Shigaraki, who could have unleashed an unfathomable level of destruction upon the planet if he'd been left to run rampant. Deku sacrificing his quirk was what allowed him to become the greatest hero in the world, he embodies what a true hero really is; someone who would sacrifice anything, even their greatest gifts, to save another life. I agree that Deku losing his quirk was really annoying especially after how much he'd grown as a character while using it, but him sacrificing One For All was what allowed him to truly become the world's greatest hero, the only person who could have stopped Shigaraki.
