I seem to recall one such quote, but I can't seem to find it now. Do you have it around? It doesn't seem to be in Anamnesis.
As for your 1, not necessarily. Beings of similar aether density already exist in the world, namely the multitude of familiars.
We weren't efficient against Meteion because we had torebuild civilization multiple times and had incredibly foreign motivations compared to Ancients. In fact, out outlook on life is quite similar to Venat's, and I suppose Azem's as well.
So no, I argue to integrate them into society as full fledged ancients who made a sacrifice in order to fix the Meteion problem, and they may choose to be rejoined after their purpose is over or continue as mortals in that society.
Even if they were to create a society, I doubt Emet-Selch and the other Ascians would have much issue with how things are done in Sharlayan. A civilization guided by Ancients wouldn't necessarily end in tragedy.
And then, if mortals tried to go full Ancientsong way, how would it end? Rejoin, and become Ancients? Well, one experiment failed, 12000 years of experiment to go!
To be clear, I don't think the writers even imply that Venat's way was the only one. But it's something part of the community thinks, despite constantly failing to give proof. Which is natural since no proof can exist, given it never even had a chance to happen.
The game takes place in a world where Venat did sunder Etheirys, and since our timeline cannot simply be erased due to 10 years of content taking place in it, it had to be resolved this way. They also probably didn't want to do the whole "change past to create a safe timeline" a second time after Shadowbringers, and so had Venat act the way she did. It shows us a flawed Venat, but it works, characters obviously not always making the best decisions.
Even in the liveletter, when Yoshi-P breaches the subject, he says it's something Venat believes, not that there wasn't any other way. She sees Zodiark being summoned, and comes to the conclusion that they'll just go toward their end, envisionning them ending in a similar way as the Plenty. So she decided to sunder everything.
Yoshi-P even mentions that Alphinaud was right when he contested Emet-Selch's right to judge mankind, and that the same applied to Venat.