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

[Absimiliard]

And even then massacres don't usually beget new life. I'm not quite sure we have a a suitable word for what it is except a sundering. Maybe that's why the game calls it that, actually.

I might briefly note the sundering did not actually split its victims up into new life the way many people seem to think. It tore them apart spiritually, aetherially, and physically before haphazardly reconstituting what remained into wholly new entities, per NieR Re[in]carnation's very much canon crossover event. These unfortunate beings weren't even sapient at first, incapable of even the most rudimentary of communication. About the only thing they could do was exist in a state of absolute agony until however much time passed. Even the ascians could not communicate with them despite their innate ability to speak with anything that possesses a soul. Gives you a pretty good idea of the kind of shape the sundered were in.

It's also worth pointing out how similar this is to the way life in general works in the setting. A creature dies, and its soul returns to the lifestream for X amount of time wherein it will either be broken down into raw aether for a new soul to form or sent back to reincarnate as it was, albeit without memories of its previous life. The physical component... well, I should think that one is fairly self-explanatory. Anyway, does this process mean people on Etheirys that die aren't really dead? After all, everyone born is comprised of the spiritual and physical remnants of people and things that preceded them.