Disappointed in one Endwalker Aspect [SPOILERS]

[Cilia]

Having just rewatched the scene on this character, it's not clear what the Ancients in the "Sundering" cutscene intended to sacrifice. They appear to be offering themselves, but the scene isn't literal, so mayhap the sacrifices just weren't rendered or shown for brevity's sake.

Either way, her main arguments against the faithful is that sorrow was always there (they'd just been spared it for a while), and that sacrificing the future to bring back the past is unwise and weak. She also sunders the world not because she has no faith in mankind but because she has faith in mankind, even though they've lost all faith in themselves and refuse to (ahem) forge ahead into an uncertain future. By sundering the world and eliminating the temptation of using Zodiark for whatever they want, she successfully forces mankind to rise to Hermes' challenge (or less charitably gambles everything on being able to do as much).

Emet-Selch never capitulates on his ideals, but he does acknowledge that Venat's methods had succeeded where his own would have failed.

[Cleretic]

Having just rewatched the scene on this character, it's not clear what the Ancients in the "Sundering" cutscene intended to sacrifice. They appear to be offering themselves, but the scene isn't literal, so mayhap the sacrifices just weren't rendered or shown for brevity's sake.

Love the rest of your post, but it's worth clarifying: the Ancient crowd in the post-Elpis cutscene are almost definitely the second of three intended sacrifices that we learned about from Fake Hythlodaeus in Shadowbringers. The detail that there were three sacrifices was extremely lost at the time, because the second one only came up in a single text box in a very long infodump while the first and third were very clearly important, but the crowd scene matches up to what we heard of the second: that after the beasts of the End of Days had been stopped by Zodiark, the world was still in a pretty bad state and they beseeched Zodiark to do things like 'stop the fires' and 'make the wind blow again'.

Afterwards, we can reason that while this was an absolutely well-meaning sacrifice, it was the wrong one, and it was possible for them to solve this problem in a smaller, more sustainable way. The Tales from the Shadows story about Azem actually tells us this; it was quite possible to use creation magic to solve natural disasters, it was just that Azem was the only one that was actively taking that angle.

...incidentally, the conditions around the second sacrifice actually resemble the things that happen when elemental crystals in Final Fantasy games go awry; Final Fantasy V and Bravely Default 2 both came to mind for me. I feel like that was intentional, but I don't know if it was 'easter egg for people who recognize it' intentional, or 'parallel problem so you can tell they picked wrong' intentional.