It is probably a stretch with the EB comparison, but IF he reaches his full potential and is in the right situation, then I could see him as a pre-injury EB type of player. Of course, I can see him becoming Big Baby 2.0 too.
Elton Brand was a #1 pick. He was a rookie of the year. Dude was always a major contributor. Sully was drafted #21 for valid reasons. He could end up a starter, but I don't see any star potential in him.
I don't see the Elton Brand comparison either. That's kind of a ridiculous comparison because Brand was a physical beast before he tore his achilles. For one, he has a 7'5 wingspan even though he's only 6'8.25 in barefeet. Even in the NBA that's an anomaly. Two, he was one of the best running big men in the NBA. He got a lot of his points from simply beating his man down the floor and getting open for short jumpers early in the shot clock. Sullinger can't match Elton physically or as a shotblocker.
Brand put up hall of fame caliber numbers before his injury. There is no way Sullinger is capable of that.
I see the David West comparison. Their releases are similar and both do their work offensively while barely getting off the floor. As strong as Sullinger is though, I don't think he's as capable as West is of keeping his defender on his backside and playing under control. Sullinger's post game is raggedy while West is pretty smooth. Sullinger is a better rebounder but I think having less length and core body control makes him an inferior offensive player than West.