Sheldon hasn't lived up to being the number 5 pick in a draft, but he's already put up better numbers than Leon ever has or ever will.
How so? Leon has put up better scoring, rebounding, and field goal percentage numbers. Williams averaged 4.1 points and 3.4 rebounds last year. Williams is a pretty good defender and rebounder, but he wasn't signed due to his numbers.
Yeah, honestly, it is a tough comparison, mainly due to the situations they were both in. Williams was on bad teams, and therefore had more opportunity to win playing time than Powe did, Powe on the other hand was playing with extremely talented teammates, who helped to hide some of his weaknesses, and make him a better player.
Really, this should be a very interesting experiment (if Williams even sees the court much...there is a lot of depth in front of him). In theory, Williams should be a much better player on a team like the C's than he was on Sacramento, Minnesota, or Atlanta (he played there before they were good). On those teams he was expected to be more than the roleplayer that his skill-set dictates, but now he can simply do what he is good at.