In a group of 10 mobs, it's absolutely optimal to be hitting Ring of Thorns (even out of combo) or Doom Spike than any sort of mock "AoE" you might try by using single target.

Your "AoE single-target rotation" should also completely eschew Phlebotomize. DRG is the one Job where spreading BOTH DoTs is actually sub-optimal to maintaining HT>CT>CT>repeat with no Phleb in-between at all. 4 gsk per minute = 800 pot per mob per minute = probably 2-3 on any given pull you have BotD for.