Angela said in the very beginning (season 1) that Peter was weak. You can really see how gullible and weak he is (not literally of course), he relies on Nathan for most of his decisions. I think Kring made it really realistic and he did a good job with Peter. Peter can be very powerful but the downside of his being powerful is that mentally and emotionally he is weak.
'HE'S NOT STUPID guys, he is just weak. And I think that's fine. We don't want him all powerful both in mind and abilities...that'll be TOO PERFECT. And in this world, there's really nothing perfect.
So those who said that Peter is stupid, you need to dig deep into his personality.
