While this may be right, Andy himself says that doing the hard physical work gives him confidence. I guess it's a difficult question of balance as he certainly came up short earlier in his career because he lacked sufficient physical fitness.
He needs to be a bit more confident then rather than manically hitting the gym and wearing himself out, but at the same time you have to be seriously fit to be on court with the likes Nadal and Djokovic. So there is a balance for sure.
I just think that he should gain confidence on court more because he is so talented on it with a wider skill set than Rafa and Novak.
He's more like Federer than these two ball bashers when all is said and done.
It might help him feel more comfortable against lower ranked players at the start of tournaments.