I think the main thing with Williams that is causing doubt is that the big team wins weren't there mixed with what appears to be an exceptionally deep QB class. There's a good chance, based on the eye test, that up to 7 or 8 QBs on this class will be difference makers. However, it's just so hard to pick a "guarantee" like Luck, Stafford, and a few others.
I also think that if this was last year, the Bears taking Williams would be a "no brainier", but the depth of this class mixed with his final college season are casting the doubts. Not only that, but you have what seems to be an exceptional WR and OT class as well. The Bears have a phenomenal chance to make leaps next year if the puzzle pieces fit.
Lastly, that fleecing of Carolina last year also skews our views on everything. If we get some team to give up the farm to move up again, it would be hard not to take. That's why I really hope Washington or New England take a shot because I feel like we can get another top 10 pick again next year if we flip flop with with on them. In the end, none of us really know (even if some of us claim to). That's what I love so much about the draft.