Dungeon xp isnt bad, but yeah, it doesn't come close to FATE. Its a 2-3x factor I'd say. Maybe more. Depends on the level of FATEs and what zone you are in. North Thanalan for instance is probably on the order of 5x faster than doing dungeons. But if you are level 15 lets say, then yes, dungeons aren't bad, but they are still inferior to doing FATEs.

I'm still waiting for someone at SE to wake up and address this issue. Of course, I've said the same thing about this guy spamming in Uldah for the last 4 days on the same character name without being deleted...