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

[Katoar]

Because she hid what she knew from her people and decided to cover it up entirely by sundering them instead of telling them what she knew so they could devise an actual counter measure to Meteion.

It's like a Scientist that covered their mistake in a project that ended up killing people and only years after the fact on their deathbed do they start to tell the truth of what happened.

If she tells them all that she knows about the Final Days and works with the Ancients to successfully avert the looming tragedy a time paradox is created. The Warrior of Light would have never existed. No one would have ever travelled back in time to inform her of the calamity that is yet to unfold. Venat will not have been able to avert the Final Days because she doesn't know anything about them. And we are at the place where the Ancients never survived through the Final Days and everyone either died out or sacrificed themselves to Zodiark because Venat didn't set the world asunder because she held to no hope for a brighter future since no Warrior of Light came from the future to her time to inform her of what lies ahead.

Venat having to stay silent and let the calamity unfold was the least illogical way of preventing or handling the Time Paradox created by our Time travel.