I always find the discussion of players being 'potentially world class' a bit funny.
Loads and loads of young players look ridiculously good for their age, but as they grow older the experimental part of their game is put on a leash, they the gap closes and they look quite ordinary (in the group of players capable of class due to natural ability, but not at the top table):
Quaresma, Anelka, Nani, Joquain, Robinho, Wilshere... and more that I can't think of right now. And they all end up as very good but not the world class players they threatened to become.
Heck, even Fabregas and Rooney are up for debate.
Some expect Pogba to dominate midfield for years to come. The likelihood is that he'll stagnate quite a bit, the gap will close, and come the next World Cup he'll just be one of a number of midfielders at a similar level.
Same with 'future Ballon d'Or winner' Isco. The gap will probably close, and he'll be good but not as good as he was in comparison to his age-mates a year or two ago.