I think you've missed a couple of points. The first is that Harry has spent years with the Dursleys pounding "Don't ask questions!" into his head. And the grownups beyond the Dursleys (his teachers at school, for example) don't appear to have championed him much beyond insisting that he get glasses. He hasn't been given a lot of books to read, hasn't ever been encouraged to develop his own interests, doesn't go on outings, doesn't even have any friends to stimulate his mind with conversations. Not until he gets to Hogwarts. If Harry's learned anything from his life before Hogwarts it's that when you put your head up someone tries to take it off. That sort of life doesn't make for a scholar. It makes for a kid who does what he's asked to do and hopes that no one will punish him for doing it wrong.

Not to mention that he doesn't value himself all that much. Year after year he takes stupid chances with his own life whenever he's convinced that if he dies he will have saved others. :/