I think it matters more who is the better player. Athleticism though helpful is not what basketball is about. It is a game of skill. If you aren't athletic and can put the ball in the basket, you are a better player.
but for the sake of your post, here's my 2 cents worth:
Right now, I think Curry is more athletic. His body is more mature, he knows he has to lose weight and he is gaining muscle. Diop is about 2 years behind Curry. Diop's nagging injuries are hampering him from physically developing a man's body. He still has too much baby-fat. Injuries can change any player in an instant, but putting that threat aside for the moment I think in 4 years Diop will be a better "athlete" than Curry.
But, at the end of both players careers, I think Curry might be considered the better player, but neither will be mentioned in any "all time greatest" lists. I think Curry will end up with a higher career scoring average, Diop will have a higher career rebound and block shot average. Diop has wonderful timing on his blocks.
Personally, I would like to see both players excel. If that happened, the balance of power would shift back to the East, cuz Shaq won't play much longer. (I think he will retire from basketball way before he has too. He will win a couple more titles, then call it quits and go Hollywood or something.)