Someone recently told me that ALL AoEs have the same damage decay that flare and holy have, just those two skills in particular mention it in their tooltip. I did some experiments to test this (pulling lots of overworld mobs and casting Fire II the looking at the battle log) and i didn't notice any particular decline to the damage i dealt with increased targets, while it was noticeable with Flare.
Am I missing something or was this person incorrect? It might just be because Fire II is a smaller potency and I was attributing the damage difference to min/max differences as opposed to decay due to the small disparity.