The thing with introducing a new avatar is that it has to be situationally good, whether we like it or not.
If it's bad, then what was the point?
If it's better than every other avatar, then the others will never be used (or it can be this, but a meteor/arise style scroll drop).
So it has to be good for certain situations, or have certain weaknesses, for example much better DD capabilities, but remove the -50% damage taken, that way other avatars are still better for soloing hard NMs.
Personally, I'd like to see Cait Sith be slightly more powerful in general than other avatars, but have no element, so other avatars are still better choices vs mobs with a particular favourite elemental attack, but Cait Sith is better vs more physical monsters.
I don't see Atomos having any use whatsoever. Odin is useless outside of an exp pt in abyssea where you can spam revitalisers and ISL chests. If you're doing zerg content, Alex is the only way to go for Astral flow. If soloing or low-man/all pet jobs, the new 2 hour will own. We don't need another 2-hour only avatar, unless his move will be to grant an alliance-wide embrava effect, or similar DD-type buff. To be on-par, it would have to be 100% double-attack with an att/acc or str boost or something similar.