This is Part 2 to my post, couldn't fit it all.
I do believe that the Ancients could have come up with a counter to Meteion so long as they were made aware of all that Venat knew. At the time, Meteion had just left the planet she couldn't possibly have been the seemingly nigh-unstoppable monster we fought tens of thousands of years later.
I suppose the bottom line is that Endwalker just felt empty and devoid of meaning as a whole. It attempts to instill us with what it thinks is meaningful but like with all media its value it subjective and I feel for a lot it just didn't jive well with them.
For me in particular, I felt affronted by the patterns of thought and justice personas it attempted to force me to follow. The Ancients were demonized on multiple occasions in the plot and by the fandom and I despise dehumanization. I suppose I had faith that this is thinking common decency but I guess I underestimated how many people would willing to ignore or justify it when its not aimed at their favored demographic.
In regards to Venat, I suppose I never quite realized when the world warped the perspective around the "ends justify the means" philosophy because to my understanding that's always been a budding villain's motive and I can't really fathom how many people see Venat as a hero despite that.
For me, I rather distrusted her from the beginning. All the evidence we receive in ShB and before, then we learn of her "love" and yet her motives are that. I can't honestly reconcile the two.
Then there's the time travel plot point, which feels like a betrayal in and of itself. For all time travels faults, I personally felt that the whole point of time travel was to try and save people, but then they made it a closed loop unlike G'raha's old timeline and the entire time in Elpis's purpose seems to be serve no purpose but to build up Venat's positive character even more.
So I went in thinking maybe Elidibus was wrong and I could save the Ancients but all I accomplished in the World Unsundered was taking active part in their assured annihilation? Not enough was it that they are gone, but now Square says that it always meant to happen and of course I have to be a direct part of it now.
That's a step way too far, it goes beyond forced characterization at that point. Now my character is being forced to destroy her own people and of course she totally agrees with it? No, she wouldn't.
So, yeah.
Tldr; the Ancients are my true people, not the Sundered and Endwalker was one big nightmare for me that forced me to commit virtual genocide, be okay with it, offend my moral values, wank the other person responsible the whole ride, and generally commit numerous crimes on my person at the hands of Square Enix.