Endwalker's story had me, but lost me. Ethical issues especially (spoilers)

[Alleo]

That's for us, not for the Ancients. Though I suspect reconstituted Ancients might actually care about other worlds due to their experiences while sundered.

Emet says that the remaining inhabitants of the source would be offered for the exchange of the Ancients souls. So bascially the only ones still alive would be the few Ascians with their huge emotional baggage and those that lived as a "god" for a very long time and who bascially went asleep after the sundering. None of these two groups sound like good canditates to defeat Meteion.

Edit:

Also as far as we know these now fully rejoined people should not just simply get their memories back. We did not just get memories when Ardbert rejoined with us so I doubt that it would happen with a full rejoining. On top of that these survivors could 1. be newborn souls since not everyone is an Ancient and 2. could be an Ancient that still loves the current world.

I really doubt that the survivors would be all too happy after all these people had loved ones too which the Ascians killed to get their past back. All of this of course if they survived which I doubt when you recall Emets words.