If anything, doing the side quests in Elpis doesn't help seeing them as "unable" to learn, grow and change quite the contrary...Most of them were eager to see and try news ways of doing things and thinking. What they needed wasn't obliteration but matter to grow from. Things grow with and according to the soil it's given, not from nothingness. Presented as they were, if they had knowledge of not only what caused the final days but how many civilisations ended, there's no doubt they would have re-evaluated their ways.
It's quite a disservice when the story tries to kind of force onto the player that the ancient humans were doomed anyway as they had no room for growth unlike the sundered humans. Even going to length as putting Ra-La civilisation as a direct mirror, which I saw as a desperate attempt to be convincing. Moreover, it didn't seem like they lacked purpose either. Each ancient we interact with in the msq had different aspirations, each of them already had a personal purpose for their lives, so this argument falls flat too on my end.
They ended up painting the ancients as many things that are sometimes opposite, which ultimately make Endwalker hard to go along with.
I can understand what Yoshida said about Venat's actions as very ancient, but at the same time this too clashes with their depiction. They were a scholarly civilisation, where no one would be encouraged to take drastic measures by themselves, but rather discuss together before taking a decision. I can only think of Venat and Azem as people who'd regularly decide and act without the consent of the many.
It might be a personal view on it, but the many contradictory details might be why some aren't satisfied with Endwalker's story, and why it leaves so much place for argumentation.
Somehow, instead of leaving a feeling of hope as intended, Endwalker struck me with fatalism.