Official character book only covers between Chapters 1 to 88. This is where All Might and other heroes assault the League of Villains to save Bakugo.
So if you consider fights that Midoriya was in, until there, I think you can see the pattern. Midoriya usually breaks his bones while fighting. Yes, there are some fights where he doesn't, but not that much. The fight between him and Muscular is a good example.
Even if you defeat someone that is so powerful but destroy yourself in the process, that makes you a liability. You defeated one big guy, good. But if a low-tier villain can one-shot you after that fight, could you really call yourself that powerful?
Only a handful of people know that Midoriya inherited One for All. To others, he is not super powerful. The Tournament Arc is a good example of it. How many pro heroes were willing to recruit him?