This was a good read on what you should be doing once you reach level 50. It look's like the higher tiered dungeons(AV, CC, DD) drop tombstones which you exchange for Darklight gear. I don't see Relic armor dropping from coffers or Darklight dropping for free either like this person speculates, but I can neither confirm or deny it. I have gotten tombstone drops from each dungeon though. I also don't see relic weapons being a necessity for Bahamut either, but this is still some good info.
Kedo replied
630 weeks ago