He can glide past players, the problem is that that is nearly all he does - dribble dribble dribble, then hesitate, then pass. Like Parker, he needs to first-time pass it so much more quickly and incisively. The extra touches are really smothering our counterattacking opportunities, especially in comparison to an intelligent passer like Modric or even Cabaye, and I think his drop in performance at least partly comes from teams reading him better now and simply "pinching" the ball off him as he inevitably tries to dribble forward.
I am not sure if this is an issue of personal playing style, or technique, or vision. From what I have heard from Fulham fans, they too believed that his biggest problem is his tendency to take too many touches and release the ball too slowly. (Then again, I think all of our players have issues when it comes to one-touch passing, even relative to some midtable team, and I have no idea why this is. Players lacking in passing technique like Dempsey and Walker really don't help, admittedly.)
I'd like to see Dembele work on this in training, replacing him with Holtby in that deep position for now; I really think Dembele is either tired or carrying a minor injury so a rest on the sidelines will do him some good anyways. Holtby strikes me as more of a Modric than a VdV, at least partly since his goalscoring record's never been that great, but also because he is perhaps the only midfielder of ours atm who prefers to "knit" the play with quick, progressive passing than to dribble; he isn't anywhere near Dembele's defending atm but he isn't a bad heel-snapper either.
Like I've said before, I don't think Dembele is a bad player, just that his weaknesses are really exposed in a team that is already lacking in one-touch football. His defensive qualities have been really important in freeing up the likes of Bale and protecting our defensively fragile fullbacks, and it's really our defense that is carrying us this season. However, we consistently have issues carving out clear chances in open play this season, and as a crucial midfielder he is a part of the problem too.