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

[Theodric]

Many cases of genocide have been framed as a matter of necessity and survival. It doesn't cease to be an act of genocide solely because there are those who stand to benefit from the atrocity in question. Given that the ancients no longer exist as a species it isn't really up for debate as to whether it qualifies as such because it fulfills the criteria of the definition.

Certainly, the Rejoinings are considered to be an act of genocide and those are a matter of reversing the consequences of Venat's actions. (Though I'd add that even the Rejoinings are something that Venat has an indirect hand in given that she knowingly left room for Emet-Selch to be spared despite being well aware of what that would result in...)