My opinion on DPS queue times stems from a couple of factors.

1) FATE's have easier and faster XP than dungeons. People will naturally gravitate to the path of least resistance.
2) Dungeon rewards (gear) are not really needed and are a pain in the arse to get, especially if you want a certain full set. You can farm the Fates for seals and buy GC gear, which in most cases is on par with or better than what you can get in dungeons AND has a set bonus, which dungeon gears do not have.

All in all, there is absolutely NO reason to queue for dungeons other than story progression.