None of the 4-man dungeons require any specific DPS to complete. Heck, the only content in the game I know of that absolutely requires one DPS over another is Turn 4, thanks to the Knights/Soldiers (you can do it with 4 Physical...I have yet to hear it done with 4 Magic. Don't say ADS, since SCH and PLD can Silence too...)

I'm leveling BRD. 3/4 of the time in the Roulette the other DPS is another Ranged; THM/BLM, ARC/BRD or ACN/SMN. I get a PGL/MNK or LNC/DRG about 1/4 of the time.

So...why is ranged taking so long? The game wants to balance things out; 1 tank, 1 heal, 1 melee, 1 ranged. Cover all the bases. Thanks to a shortage of melee (because so many people don't know how to play them properly, and ranged is "easier" to play), ranged are getting longer queues. But...at the same time, you still get a lot of 2-rDPS parties through the DF, which means there is a huge difference in the ratio of melee to ranged...If there wasn't, queue times would be about equal for all DPS.