I do all the content in a game whether it's below my level or not, because I do it for the story. I don't need someone to reward me for enjoying the story.
Why the hell should we level slower? Leveling is a keep-players-playing mechanism anyway, in moderns MMOs it shouldn't even exist. It's an utterly pointless system of a bygone era. "Oh, you want to go there? You can't, you're not high level enough." "I'm gonna be high level enough in 2 months anyway what's the point?"…