I think it would be wise to lower our expectations of what we will get from Lewis. Not only is he coming back from 2 surgeries (one major one), he hasn't done much in the way of football activities for over a year. The team has had close to 100 practices since TC, and Lewis has had under 10. To say he's a little behind, is an understatement.
Last season, for a short time, Lewis showed that he CAN be a dymamic player in an explosive offense. To expect the same kind of explosiveness after such a serious injury and a long layoff would be unfair to the player. Where he was great last season, I'll settle for good.
That being said, where he CAN be a big upgrade for the offense is by being a legitimate running threat when he's in there. White has been an overacheiver and very effective in the passing game, both as a receiver and blocker, however he still poses no threat as a runner.