You can accept quests a good few levels higher than yours if you have a crafty class up there at least, but it seems like you can't return/complete the quest before reaching the actual level of the quest. Why is this?

Say that you're looking for a challenge and trying to level up with a friend or three without just boring yourselves to death by spamming FATEs. You could go to areas 3-5 levels higher than you easily and do the content there. What's the point of not being able to complete quests just a few levels higher than yours in the first place?

I understand the need to make you unable to return some of the quests heavily above your level that way due to being able to switch jobs, but come on. Overdoing it pretty heavily.