I really don't know if one way is faster than the other. I'm not really concerned about my personal DPS going up if AOE'ing will slow down the pace in which things die.

I'm only looking at the perspective of a BLM and usually playing with a person that focuses single target. By the time the first mob is down, if I'm AOE'ing then the other 2+ mobs will typically be at close to half of their life left. I honestly can't say whether or not the fight would have progressed faster had I just focused on one target at a time since my burst damage as a BLM is pretty high.

Maybe I should run a stopwatch between two of those 3 pack gargoyle pulls in AK and see the difference between single target and AOE damage.

I just know from a BLM point of view, my danger of taking threat is pretty high regardless if I don't have Quelling Strikes ready. A mob will usually be dead before it turns its attention to me with a relic tank, but tanks with lower ilvl gear struggle to keep up with my damage. For AOE, tanks have to keep up with Flash so that things don't peel off of them. This is mitigated a bit by me using Quelling Strikes and I tend not to AOE if it's not up as after a few Fire 2 casts things are going to be running after me.