Hughes would do better in a no-gi grappling match with Renzo than GSP would do in a NCAA rules wrestling match with Koscheck IMO.
But that's not the point. The point is, who really cares if Kos is the better pure wrestler? Just like nobody cares that people like Almeida and Renzo are probably better pure grapplers than Hughes.
If that was their professions, then it would make sense. But GSP is not a wrestler, he is an MMA fighter and he beat Kos. Saying Kos is a better pure wrestler doesn't make a bit of difference.