I find it really sad that the requirement is to have one of each role and not just one class. Anyone considered worthy to be a mentor should have a basic understanding of how all the roles works even without having them leveled. Personally I have both tank and DPS leveled and have quite a good understanding on how healer works, but I lack interest in leveling and play a healer and therefore can't use the mentor system. As for having a deeper understanding of the classes you would have to have played them anyways and the requirement in that case should be to have all classes at 60. Also having the 3 roles at 60 doesn't matter, there's a lot of players who simply leveled through FATEs and know less than a player that doesn't even have the class leveled.