It doesn't need to be slowed down. But it needs to change somewhat so it actually teaches you to play your class.
Don't give me the crap that somebody leveling 1-85 learned how to play, because they didn't. Rotations and playstyle change CONSIDERABLY when you go from 82-85, because in the lower levels weird stuff is way more effective then the normal rotations you're going to use after you're done leveling. Just take shadow priests and smite healing. Dang, till lvl 80 it's more effective to dps as smite-heal than as shadow in dungeons, which means you learn nothing about how real healing is done or how shadow dps is done. And once you ding 85 and step into your first heroic dungeon you can't play neither and have to learn it. Similar for most other classes. But in my opinion this learning process of how to do it right shouldn't be done as late as lvl 85, it should be done earlier.