The nature of the Sundering has been spelled out in a Nier Reincarnation side story.

[Cleretic]

I hope this stuff will settle the "was the Sundering murder?" question in favor of "yeah", since it's clear it completely destroyed people's identities and even physical forms, but I kinda doubt it.

Honestly, that argument was always kind of a weird decoy anyway. Because sure, the sundering is murder, but you know what else is murder? Murder. And the Ascians committed a lot more murder.

It's a weird play for equivalency that then refuses to admit equivalency.