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

[DiaDeem]

Is it really "killed half the population" when they did it in their own volition?

Oh no, even if willingly, they were sacrificed, thus got killed. Not saying it wasn't noble or anything but they most def got killed lol.

This, I can agree. The Ancients were flawed and not perfect, what annoys me is that they're judged on completely different standards for their mistakes than the Sundered or our own mankind.
Hermes apparently didn't receive the amount of mental health care he needed? "Wow their society were a bunch of evil unfeeling fascists who deserved to die".
They had to make difficult choices to ensure the star would survive? "Their kind was doomed, it doesn't matter if Venat killed them."
Try to apply the same logic to humans and see how cruel this would be

As someone who'd do anything for her family, I actually relate more with Emet than I do with Venat at a personal level. I feel a lot people are quick to pass judgement without realizing that being on their position wouldn't make the choices as clear cut and simple. I do wish Venat told Emet about the Final Days right away, and wish she brought to a vote if the sundering was a good idea at all. I get that she wanted to introduce pain into the world to prevent their society from becoming apathetic to everything like the Nibium from the Dead Ends, but... she didn't even give them a chance to show they could do better. I'm not entirely sure what the full intent was behind how they painted each character, but how grey they all came across to me is what makes them the best characters in the story. I guess the one thing I would have wanted was for the game to question Venat and her actions a bit more as it did for everyone (ancients) else. I do like them all in their own way, for the record.