I've always been convinced that... he's just not very good. Wesley Matthews would have fit this system perfectly.
Eh, too early to tell. He still looks like he doesn't have his legs under him yet. I'm definitely impressed by his length -- he's like a slightly smaller version of Deng with his low center of gravity. In the game verse Orlando he had a number of plays where he tried to pull off moves and you could tell his legs just weren't there for him yet.