There are a few problems with his weight. First, he doesn't have the quickness to defend a lot of 4s in the league. If he was at about 260 he would be much more effective and he could play the 4 full time which I think would be his best position.
Second is the combination of his age, his lifetime of weight issues, and his consistent weight gain. He was 268 at the combine and was considered overweight. He gained weight during his first season, gained weight during last season, and looks to have gained weight this offseason. I'm guessing he's pushing 300 now. That's a scary pattern for a 22 year old as it will only get harder to keep the weight off. Shaq by comparison was quite ripped at the same age and gained his weight gradually over a twenty year career.
Third, it's only going to add to his back problem.