The whole point of having a dungeon roulette is to put players where they are needed according to demand. Artificially cutting the roulettes up like this would just divide the player population pool into smaller cliques, resulting in longer queue times for everyone.

No high-level players will queue for "Beginner" roulette, I guarantee it. New players and those who want to level alt jobs will be punished for it. And then the game will begin its downward spiral into death.