Endwalker was a great mess(SPOILERS)

[Lauront]

What I mean by unable to adapt was that after Zodiark was summoned and the 2nd sacrifice happened there was a brief moment of peace. Theoretically that was the tipping point more so than his creation (theoretically because tempering inherently threw a wrench in that, the convocation were sol from the moment they "saved" the day). In that interlude the survivors debated what to do next. The convocation was going to push for sacrifice #3...and thats where everything went to hell. Had everyone been able to accept what was lost and made due with who they had left they wouldn't have needed to have been sundered. It would have been painful to accept permanent loss of those who gave the ultimate sacrifice (rip Hyth ;-;7) but it could have stopped there. Theoretically. Poor Elidibus drew the shortest stick in the planet's history :c

Elpis' ending cutscene and Ultima Thule are ultimately about people who locked their legs instead of adapting. The story is a little clumsy in the message because the writers inexplicably really wanted a self fulfilling prophesy/bootstrap paradox, but I'm pretty sure its trying to tell you that even when you're hurt, scared, sad, etc, you need to put one foot in front of the other and keep moving forward.

That may well be the point the writers are trying to push, but it is understandable to me why the Convocation - and their broader society - would refuse to adapt in that way, because putting aside any other desires for their return, if those souls were stuck inside Zodiark, they'd effectively be in a form of purgatory and deprived their connection to the star. Certainly in the story up to SHB we're not really given any reason as to why they'd need to be sundered, other than the opinions of Venat's faction over whether the new lives should inherit the star. The only rationale I can see comes post-EW (and only after the Elpis events, i.e. this would not have been knowledge available to them in the timeline prior to this), and even then only if you assume that had they been told the full story (which they were not, because the only person who knew it did not want to alter the timeline), they'd still have pressed onto their potential doom. In the absence of that we're stuck with "what ifs" as opposed to anything like a justification. Tempering is much of a muchness given what was revealed right before the launch of Ragnarok. Certainly one can make the case that, after 12k years, it affected Lahabrea due to identity erosion and Elidibus due to wilfully allowing memory loss, but Zodiark was not actively using it to command them to do anything, because he was not that kind of primal. He was designed to have a controller.