It isn't as simple as "one option or another". Not splitting further into cooldowns, currently there are 3 types of AoE (think [ability]Spiritfire Beam[/ability], [ability]Arcane Explosion[/ability] and [ability]Thunderbolt[/ability]) and each has its own "yays and nays".
What we'd need is a formula that balances out the damage at each stage of the encounter, not only the beginning or the end.
The AE-likes are supposed to do that, but in practice it doesn't go very well because spammable AoE moves are in general lame. And who the fel designed the [ability]Flux[/ability]? (Don't look here, there are always huge values at the ability pages

)
I know that's because of [ability]Prowl[/ability], but the simultaneity never was a reason for breaking other abilities.
Okay, so how to build THE AoE ability from scratch?
- It has to have a reasonable cooldown -- not too short, to discourage spammability, and not too long, because of the big impact seen with Graves himself. Two or three rounds are enough.
- It should retain the total amount of damage dealt regardless on the stage, but in another way than the 1:1 split.
- The backline damage should be coverable by currently available AoE heals, like [ability]Bleat[/ability]. There may be some measuring problems because of breeds and healing RNG, but I believe that there is a good approximation. An ideal clone would be boring anyway!

- The damage dealt to the last survivor should correspond to the damage from a standard ability for that cooldown.
As EU buddy [url=http://www.warcraftpets.com/account/profiles/Vakeetah/]Vakeetah[/url] said, the general formula goes that way:
[BASE + (BASE/20) x AP]
For [ability]Bleat[/ability] (The model AoE heal, with not the highest HPR, but decent nevertheless. Warning: a 4R cooldown!), the base is
15.
The further calculations, sadly, I need to leave for someone more familiar with theorycrafting, or just write them another day. ^^