He can not gain another pound of muscle and never make a 3pt shot and still not be a bust because he is a generational defender.I'm going to disagree there. He can get bodied by more muscular players and traditionally Bigs don't make a living on the perimeter in that regard. Give him some time to get a bit of mass and he should be good there.
Do I think he'll bust? No. It is possible? Yes. But he went to one of the best environments possible, so it's not likely. However, nothing is certain.
It's quite literally impossible for him to bust unless he tears multiple muscles.