The point is, being in the so-called world XI isn't the sole definition of "world class". Neuer & De Gea are, to all intents, both world class. There's only one spot for a keeper in a team though, it really doesn't relegate either of them to not world class.
As for Pogba, I would agree that he's not yet in the tier of Modric, Kroos et al, but he's definitely on his way there, and I think it's very unlikely that he doesn't reach that level in the next few years. Whether that's a risk worth taking, the club and Mourinho seem to be confident of.