Apparently, Sully didn't gain much athleticism despite losing a lot of weight. Only decreased his power advantage in the post. Something we'll have to wait to find out more about in the next few seasons.
No expert here but weight doesn't equal strength right? Plus if he shed the fat and put on muscle instead would he not be even stronger?
Well, there is strength, and then there is leverage. Having the extra weight does help him with leverage in the post, to be able to hold his position.
As for increasing his athleticism, I think its too early to know about that. Its not just about shedding weight (and clearly Sully still had a good amount of weight to shed after last season...he was still very heavy in summerleague), but working with trainers to build that quickness and athleticism in a way that works best for basketball players.
I know nothing about Ohio State's trainers, but I would still wager that the C's trainers are a little better.
Give him some more time with Brian Doo and company, and we will see how his quickness improves.