A group sync could help a little but here's the thing. The game has soooo muuuuuuch dialog and cutscenes in the msq that even if you make it easier to do the gameplay bits together without a friend outleveleing it to absurd degrees, you're still either going to have either the friend sietting there bored while the newbie reads through it all, or the newbie skipping it and missing out in order to keep things moving.

There's really not an easy fix to that. The quests, outside of dungeons etc where you HAVE to group up, were written largely like a single player experience.