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

[Theodric]

Yep. It reminds me of that youtube video that criticized Venat for practicing eugenics, which is pretty much what she did by artificially altering an entire population of beings by enhancing their survivability.

Yep - and it doesn't even really enhance their survivability. They're more vulnerable to despair dynamis since they are directly transformed into blasphemies. At best you could argue that she thought that a world of suffering would make them more emotionally resilient, but that doesn't even follow from what we know of real world psychology, and in the game itself you have Thavnair's skies filled with blasphemies, and the Omega side quest in Endwalker pouring cold water on it, if the fact that enough of them survived to summon Zodiark in the face of a completely unknown crisis didn't suffice to prove as much itself.

Refraining from that terminology doesn't make light of her actions or detract from what she did. But these are some very charged words, with links to some very real, absolutely dreadful IRL atrocities that continue to impact people today, as does the ideology behind them, and I do not like dragging them into a debate on a fantasy world where the topic at hand involves scenarios and variables that are so vastly different from anything we experience that it is a questionable fit to apply them here. Dividing them from the baggage and background they carry is not a choice that everyone agrees with, the resulting debate and emotional response it invokes obscures the actual discussion, and they are not needed to make the argument against Venat work.

I respect your decision not to use the term but there is enough there for me to use it as all the crucial elements for it are met by her actions. The magical aspects of it don't change the fact that it involved the deliberate alteration and destruction of her own species, resulting in the death of its individual members and attempts by her to erase memory of them... her motives being 'good' in nature doesn't change this, much as it makes little difference with the Ascians.

Sadly the game shies away from showing the immediate aftermath of the Sundering's atrocities enacted on the Ancients, instead shoving them into the NieR crossover. It is again starker when dealing with the fallout of the rejoinings. Although ultimately that's a false dichotomy, seeing as she ensured those would come to pass as well.