Statistically, Sullinger's defense has been excellent across the board. Now, some of this is the "KG Effect", as Stiemer and Bass both were statistically top defenders last year, too. However, numbers suggest Sully is doing a good job out there:
Sully's Points per possession allowed:
Overall: .73 (rank: 26th in the entire NBA)
Isolation: .62 (31st)
Post-up: .69 (32nd)
P&R Man: .92 (27th)
Spot Up: .76 (41st)
KG's Points per possession allowed:
Overall: .74 (rank: 29th in the entire NBA)
Isolation: .55 (16th)
Post-up: .63 (17th)
P&R Man: .86 (22nd)
Spot Up: .84 (73rd)
I wonder where KG's poor (relatively) spot up defense comes from. The only thing I can think of is he is a great help defender which puts him out of position to contest pick and pops.
To make some points about various comments earlier:
1. I don't think Sully is short but his lack of leaping ability makes him seem undersized when he actually isn't.
2. Although I don't expect him to get much quicker or jump much higher throughout his career I do expect him to improve his athleticism. The way he will do this is by getting stronger. David West and Zach Randolph are two players with limited verts that I think compare to sully.
3. As to him reacting like Perk when he commits a foul, I don't think it's that bad. He is getting the standard unathletic (in the refs view) treatment. This is similar to the white stiff treatment that Stiemsma got last year. As he continues to improve he will get the benefit of the doubt and won't have to argue calls.
4. Even if he doesn't block shots he is in the right place to persuade drivers not to attack the paint. This is just as valuable as blocking a shot.