I've already commented on the Pele thing but there was a time when I also thought that Dembele had greater potential than Mbappe to be fair. It only seems crazy now because Dembele has had a bunch of injury problems and hardly played whilst Mbappe has forged ahead.
I used to think the same, to me Dembele was the most talented player I'd seen in a long time, just natural gift, ambipedal, dribbling, crossing from both wings, speed, but now I'm completely off that track, Mbappe's by far the biggest talent in French football. Whether it's physical, technical, or mental attributes, he's far ahead IMO. That being said, Dembele has world-class talent but he needs to have a full season of what he's doing now for people to start to view him that way. I think everybody is still waiting for his next injury right around the corner, but at least he seems to have his head screwed on straight now (probably the most difficult thing for some to get past) and Xavi has been a huge positive for him, so the rest is just about staying fit and he'll be a great player. A move to Manchester United would probably have derailed him and they wouldn't get the player they're hoping, he's probably still very susceptible of falling back into bad habits if he's not happy.