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

[Absimiliard]

If our Elpis visit is what actually happened in the original time then I don't understand your original argument that Emet couldn't have gleaned our past from someone who saw us or the Aether. His memories were wiped and we are clearly a reincarnation but surely since it's so casual he could find it from some other subject or the Aether? And then what about everyone else who were investigating the final days? I've already asked why is Venat the single person who can solve the mystery? Bc you want to poke holes in EW or?

Her playing games with Emet doesn't prove anything. The point is she explicitly tells us she's going to bring people I to the fold and I assume she does (the Twelve??) but whatever she does fails because she can't stop the Zodiark solution...

The WoL is a fragment of Azem, not a fragment of a different version of themselves from another timeline. The events of Elpis would not be present anywhere in their being if they themselves had not been there. It's as simple as that. "Our" WoL had no involvement with Elpis or its events until the exact moment they went there, not until.

The people investigating the Final Days were lacking a significant amount of information as to its true nature. They did not know about Meteion because Venat never told them. They completely misdiagnosed the problem in their ignorance, although they were fortunate enough for Hermes and his contemporaries to wind up arriving at a workable, if temporary solution in the form of Zodiark. Through Zodiark they managed to treat the symptoms even if the cause remained unknown.

Or were you meaning people in the modern era trying to understand it? If so, then that answer is a lot more simple. Setting aside how rare the Echo actually is, there's a limit on how far back you can look with it. Modern Echo-users, no matter how skilled, would never be able to look far enough back to glean even one iota of useful information about the Final Days from the world.

"Playing games" with Emet-Selch, as you put it, was a key part of ensuring the timeline she sought would come to pass. It was only through the presence of the Ascians things could play out in a manner necessary for events to unfold as they'd been foretold. And for Venat "bringing others into the fold?" That does not necessarily mean she's told them the truth of it, particularly since we're told outright she never did. She recruited followers, yes, but none of them understood what was really happening.

Oh, right, I almost forgot:
Why Venat? Because that's the story. The story presents us with a situation wherein the rest of her people proved insufficient at correctly diagnosing the Final Days in the time they had. We can speculate all we want about whether or not they might've been able to figure it out in the span of however many millennia Zodiark bought them, but that's not the story we've been given. The story we've been given leaves Venat holding all the cards. She knew the future, she knew the true nature of the Final Days, and she even new Meteion's location courtesy of having tagged her before she escaped Etheriys' atmosphere.