I think Sully has some MAJOR potential that people are really overlooking.
His defense is rapidly improving (and, in fact, even at the beginning of the season his defense wasn't as bad as some people on these forums like to make it out to be. Statistically, his defense was a hair below average, but not terrible, now it is above average).
People on the forums like to say he isn't a good shot blocker, but if you look at his block percentage (that is, given the amount of minutes he plays, the percent of opponent shots that end in a block for him), he is actually above the league average. Not by much, admittedly, but he is a better shot-blocker than people give him credit for.
His defensive rebounding is phenomenal.
His offensive rebounding is out of this world. His offensive rebounding rate is 12.4%, good for 21st in the league. For a rookie, that's awesome.
He is averaging 1.35 points per play on those offensive rebounds/putbacks. That is good for 5th in the league. That is ... astounding. This number is skewed a bit by sample size, admittedly, but historically offensive rebounding/putbacks are a consistent stat (that is, if you look at other players in the history of the league, there usually was very little variation in their offensive rebounding/putback efficiencies over the course of their careers, even adjusting for minutes played). So you expect with a greater sample size this might regress a little, but it will almost certainly remain elite.
He does not turn the ball over.
He is a good free throw shooter, and he can hit the open jumper.
Now, his shooting percentages are nothing to write home about, they are certainly lower than I would like. Also, for being a good free throw shooter, he rarely gets to the line.
He ranks high on most advanced metrics.
Seriously, I think this kid can be a star. If he continues to develop at the rate he has and doesn't plateau, he can be a beast in this league.