There is nothing limiting Fultz besides possibly his brain and all of yours. Offensively and defensively there is nothing he can't do. yeah he is a bit undersized. But its all how the team compliments him as well.
He should be able to use his brain and realize this and use his strengths in other ways as well but thats not to say he shouldnt use his physicality or quickness. He's fine.
Comparisons are silly that way. I make them to but they are. Especially in fultz's case because he really isn't that limited.
He's not like ben simmons who hoards the ball, he pretty well rounded and plays on and off the ball. Can shoot, drive the lane catch and shoot, play physical etc. pass the ball etc..