World class is subjective, so there isn't really any way to objectively say what it is. It's all just a matter of opinion really, outside of a few players. It shouldn't exclusively be for best player in the world types like Messi and Ronaldo or even best player in his position of all time types like Buffon. But it also doesn't have to be a fixed number for each position, which would hugely underrate players at some positions and overrate players at other positions. It's also much harder to decide what makes a world class fullback or CB, or defensive mid as opposed to world class attacking players, where statistics are of much greater aid.
Pjanic and Dybala are WC for me. Well, let me qualify that. They were both world class last season. First season as such for each. SO I suppose, to truly cement themselves there, they just need to show they can play at that level year in and year out. Alex Sandro is a little further away, on the cusp of being world class, but still needs to have that consistent top level season.
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