I think Sully is still learning his place in this league. The fact that he is on the floor at all at this point in his career says something. And I think he has been quietly getting better from game to game.
The problem with Sully is that for him to be successful in the league, he is going to have to do it with smarts, skills, and trickery. And that takes time to learn. He needs to learn the tricks guys do down low to get position and rebounds (he should watch Reggie Evans). He needs to learn how to time his shots in the paint to slip them past defenders. He needs to get better at the rotations in general as a team defender.
To me though, what he really needs to do, is embrace the role of shooting from 15 feet. He has a really smooth shot from out there, but he is never looking for it. If he wants things to open up for him in other parts of the game, I think he needs to start shooting more. That will open up passing lanes, driving lanes, and it will just make him more effective in general.
I am glad Doc has cut his minutes down a bit, because it was clear he wasn't ready. But I still think he is going to be very valuable later in the season, as he continues learning the tricks of being a floor-bound big man in the NBA.