At the risk of turning this into another "what is world class? no you're wrong, that's not it" discussion, I think most players aren't really world class in most people's eyes until they play for a top club. There's a reason that when you ask someone to do a world XI it's full of Barca and Madrid players and it's probably not necessarily that they are actually the finest individuals in the world (though many of them obviously are). Their flaws are less exposed, they get more chances to score/create, win more often and win trophies so many people then decide they're world class. Is Sergio Ramos the finest CB in the world? No, probably not. Is he always up there in people's best XIs? Yes because he plays 50 games a season at the "top level", is part of what's usually a decent enough defence and he wins headers to score goals and wins major trophies. Would Tottenham's Modric have been anywhere near anyone's best XI? Probably not. Madrid's? Possibly yes.
You get those rarities that stick around at a non-top club for a decent amount of time like Bale, Modric, Suarez (though all their stocks greatly rose once they'd "done it" at a top club IMO) but on the whole what I would think most people on here would say is world class isn't necessarily what clubs are signing.
One thing I've really noticed looking at this forum for the past year is that many people are really scared to label players world class. He's a great player - but he's not world class! If Sanchez and Ozil are in any way not world class, then top clubs aren't signing world class players. Looking at Barcelona's transfer history, their only world class signings in the last 5 years have been Suarez, Villa and Fabregas and people probably wouldn't call Fabregas world class anymore (if ever? but I still think our Fabregas was definitely world class).
Neymar for example is the kind of player that I think people would love to say wasn't proven in Europe and was therefore not world class when he was signed even if he was tearing it up, but most people would probably say he was now. But if he'd spent the last 3 years in Brazil and was still the same level of player, I think people would question it.