I think people only remember Corey at the end of his career (short memories are far too common on Bigfooty). At his peak he was one of the top players in the game. Roughhead, with all due respect, has never performed at that level.
I think the fact McKernan only had the one real standout, top of the league year doesn't help either. Not to say he was only average in other years, he had some very good other years, but he never reached those heights again.
Roughead is a fine player - due to the position he plays and McKernan played - he has never got close to McKernan 96.