Yeah, Al's low post moves were world class early on. There were nights that he just couldn't be stopped one on one. That one exceptional skill makes him a slightly better prospect than Sully in my book, at that stage in their careers at least.
Al's inside game was so deadly that he pump-faked Tim Duncan to the rafters before slamming it home, as one article said at the time concerning our bright future, with him as a cornerstone. Neither is a great athlete, but no one is saying that Sullinger has the best set of post moves this side of Kevin McHale, as Tommy and many others stated at the time. Jefferson isn't really a shot blocker, but he was a double-double machine at the time of the trade. The scariest thing is that McHale taught him even more post moves after he went to Minnesota.
As for Sullinger, he is undoubtedly the better passer, and his knack for rebounding certainly trumps Al's, but he doesn't play near the basket enough for us to have enough data to do a fair comparison. His ceiling might be a Boozer/West type - not a great athlete, but a good shooter, a better rebounder than either of those guys, and a very good passer. For him to become either of those guys, though, he'll need to develop some post moves, or at least better ones. He's really wasting his talent sitting out there and chucking 3s imo, but then so is Olynyk. Wasn't post play supposed to be Kelly's forte coming out of college?