Pandæmonium story

[KuroMaboroshi]

The Ancients passed the test as best they were able and Venat murdered them before they had any chance to look into the truth behind it.[...]

The ancients "passed the test"? Did they? Maybe in so far that they did not go extinct, yes, but they sacrificed a decent chunk of their population to do so, and then proceeded to plan the genocide of whatever life would be born after the Final Days in order to bring back the souls that had been lost. They do exactly as the Ascians do millenia later when they kill off entire shards, and on top of that potentially millions of lifes on the Source each time they conduct a rejoining. Just like with Emet, their actions are understandable, but to someone of the opinion that life has intrinsic value, they are straying onto a path of evil because they refuse to accept their suffering and that a life lost is a life lost.
At that point, someone opposing them is justified if their reason to do so is protecting those lifes that the Ancients would willingly sacrifice.

Now, Venat makes the decision of sundering, thereby ending the life of the Ancients as they existed. She does the same to the Ancient civilisation that they planned to do to the new life after the Final Days, and it is okay to call her out on that. But if Venat is wrong in doing so, then so were the Ancients that would have fed more and more innocent lifes to Zodiark. At that point, Venat is not wrong and the Ancients are right, but both are wrong.

And just like the Ancient were wrong, but it is understandable what drove them to that, Venat's decision is also very understandable (again, understandable, not necessarily justified): She believes that the Ancients are headed for one of two ends - either they become the monsters that the Ascians eventually *do* end up becoming, causing more and more suffering to others because they can not accept their own suffering. They can not let go of lifes lost, someone no one would ever blame them for, and in turn inflict that pain on others. They are acting like spoiled children who have never emotionally matured enough to process their grief and move on.

The other option Venat must have considered at that point is that the Ancients are doomed to begin with, for unless they learn their lesson and emotionally mature, their civilisation is bound to end the same way all the self-ended civilisations that Meteion found were. We see this weakness explored at least two other time, first with Hermes who can not accept that live is not always fair, or beautiful, or with intrinstic purpose, and later on Ostrakon Deka-hepta, where we see another civilisation end due to a similar but instead apathy-based emotional immaturity.
So to Venat, the sundering was the lesser of three evil, though it perfectly fair to say that it was still an evil. But given those three outcomes, she chose the only one that she thought presented a way forward where eventually, happiness could be found.

I have no problem with someone calling Venat's actions evil, cause they are (though personally I believe given her options she made the right call - though absolute knowledge acquired in part through time travelling makes morale debates always tricky, cause that is not a luxury one has in reality outside of stories).
But I find this argument that somehow Venat is the source of all the bad and the Ancients might have fixed their situation ridiculous. The Ancients were already on a really dark path by the time the Final Days were over. They had already failed the test, not passed it.