I think RNG is a excellent DD job "probably" 1# if your party/Alliance has no mage support haste, BRD songs, or COR rolls for the DDs. However with proper Support from BRD, and COR which was noramlly in good Party or End of game events, the Damage potential of the other DD jobs like SAM, MNK, DRK, WAR (not in that order) can become far greater than an equally geared RNG with its own beneficial support stats.
I've noticed recently though my party and end of game event LS, has been far lacking in support role jobs, and mages that can cast haste are far too busy healing tanks or hasting tank and our 1 or 2 brd are in tank or BLM party almost never DD party. and somehow we've moved away from the rotating 2+ brd stategy so it makes it seem like RNGs rock when they are realy just ok if/when this game is played at its unlimited potential.
RNG shines best in bad party setups or unorganized end of game events.
When the game is played correctly and balanced with DD and support jobs RNG is barely top 5 DD job.