I agree with your thoughts about super!Harry, and I wanted to set myself the task of giving him some way of backing up his role in the wizarding world without it becoming a cliched fanfiction story. I'm glad you like the characterization, because I wanted Harry to be inquiring and thoughtful, and if he has any brain at all, he would see the 'gray' areas in the conflict.
I am also really happy to hear that the letter was effective--my pet peeve is the cowardice of the adult wizards of Britain!