Like I said, I don't really use the term loosely. For me, a world class player is a player that has been a protagonist for his team at the top level for a number of years. At PSG; Cavani, Zlatan, Thiago Silva; those are world class players. Then you have someone like Verratti who is well on his way to becoming a world class player.
Last season was the first season where Verratti was actually an established starter at PSG and was one of their best players(For me, he was their best player). While the previous two seasons he was more of a upcoming young prospect who played many games and showed a lot of promise, as opposed to being a key player. So he only really played at a "world class level" for one season so far.