Even with RAF, and perhaps even moreso, some dugeon clears are really great for XP. For example ZF has like 5 or 6 quests all of which can be completed by your whole team in a single run. I'd imagine this'd be like 3 or 4 levels worth of XP for an RAF team.

Also as others have mentioned, if you simply blast through quests you'll be pretty green and inexperienced with dealing with aggro, bosses, totem sequences, healing etc when you finally do get around to doing instances, so I'd recommend you do at least a few to hone your skills.