I think Peeta comes off as perfect because the book is narrated by Katniss, and she sees him as Good, as "the best of them". Everything is colored through that lens. The book doesn't dwell on Peeta's flaws because Katniss doesn't, but I don't think it doesn't mean he has them -- in fact, I enjoyed his character in part because of his issues. There's a reason Peeta considers himself disposable, and it's not simply noble self-sacrifice. I mean, come on, living for only one other person is not a good thing, or a romantic one, particularly when you didn't even know that person well. I feel like it gets genuine later on, but at the start, Katniss was someone Peeta built up in his mind so he could have some sort of connection to 'loving someone', since he never did with his family. At least, that's how it came across to me. I didn't think that was supposed to be something we were to approve of. I felt bad for him.