What's the point with that quite lackluster story in Endwalker?

[Lauront]

Indeed, we agree the writing of Endwalker is either an awkward retcon at best, or incompetent at worst. It took a reasonable, if debatable action, then shamelessly strawmanned it because uuhhhh what is nuance. Though I would like to say Zodiark did not temper Ancients in general, just the Convocation. Who were indeed respected world leaders, though in the context of a society based on debating, it's arguable how much sway they would have had on the overall population if the decisions they were making were obviously deranged.

Quite. There is no source giving any inference that their broader populace was tempered. Indeed, both they and the Convocation were divided over the matter of the third round of sacrifices, hence Elidibus emerging to mediate. In spite of the supposed effects of this tempering, Emet-Selch is able to re-consider his course in SHB, which not once does Yoshi attribute to tempering when discussing his underlying motives.

Regarding this notion that they'd just keep sacrificing forever and ever? The sole source for this is the codex in some languages. What is the codex? A piece of work implied to be authored by the WoL. Where do they get their info from? The Hyth shade and the 5.2 scene in Anamnesis, neither of which support this reading. So that leaves us with the not-really-literal walk of shame scene with Venat may try to suggest with a nudge and a wink, but it doesn't outright say that, and it suffers from the problem of being not-really-literal, and in any case, Yoshi still refers back to the Anamnesis scene during the Q&A, meaning there is no suggestion of a retcon of this earlier lore. What we instead have is an attempt at gaslighting and praying that players don't look at these older sources with too inquisitive a mind.

Of course, nothing stopping Yoshi & co from spitefully retconning stuff (or "fill in the details" with the same end in mind) if people are left insufficiently convinced of the necessity of Venat's actions to genocide her own people...