In hindsight, another thing I found...strange is how the Ancients in the post-Elpis cutscene make no direct mention of wanting to bring back those lost in summoning Zodiark; only returning things to the way they once were, which would entail much more then just bringing back the sacrificed.

I feel like they could've easily used that to make the Sundering seem more justified if they entertained the notion of there being a tangible risk that Zodiark would've given in to unrestrained desires to right all the wrongs of the Final Days with potentially disastrous consequences for the star given that he seemed to operate on an "equivalent exchange" principle and could not enact drastic change without sufficient sacrifice. With Elidibus having already separated himself, he was, as Fandaniel put it, "a being of pure instinct, wanting for guidance".