I could see Deron Williams - Marcus Smart a little bit, but I like the Kyle Lowry comp better.
Lowry is much smaller and he is a slasher, but there are definitely similarities in terms of how physical they play and how hard they pressure the ball on defense.
I don't get the Bargnani comparison? He was an average shooter and good shot-blocker, but poor at rebounding. Olynyk is a better shooter and rebounder (according to the stats), but not a shot-blocker at all. Not to mention that Olynyk has a sneaky, quirky game around the basket that Bargnani never really had.
Bargnani was actually the better 3-point shooter, but all those points are valid. You gravitate towards optimistic comps, and this one is pessimistic, it's true. Olynyk has all of the same strengths and deficits, though, with the possible exceptions of the smarter all-5 play and those sneaky used-to-be-a-point-guard moves. The similarities are clear enough. Both are mobile 7-foot centers that are nonetheless easily physically dominated and can't compete athletically; both are in the NBA because of their balance, shooting, passing, and ball handling; both are excellent free throw shooters who can't draw fouls.
Sully is not Jefferson. Sully plays in the high post and top of the key a lot of the time. Jefferson is always a low post scorer. Sully can shoot the three. Jefferson cannot. Jefferson has played center most of his career, but Sully has played power forward.
You are correct about the high-low and the three, although for the way the game is played right now, Sullinger catches deep and posts up a lot more often than most 4s (or even 5s). You are not correct about Jefferson- in Boston he spent most of his time at the 4 with Blount and Perkins at the 5 in his first two years, switching to mostly 5 in his third year. Sullinger, in his third year, has also split his time about evenly between the two positions so far (although he's playing more 4 right now).