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

[Valfreyja]

• Venat, who hasn't had her memory wiped + still remembers you from being in Elpis, quite apparently doesn't lift a finger to learn about Dynamis herself or to mobilize the other ancients to end Meteion then and there, and instead chooses to turn herself into Hydaelyn, sunder the world and the inhabitants, thereby forcing them to live with and face despair and gambling that their resilience against despair might be enough to face Meteion one day

Uh....it doesn't work like that.
You realize what that would look like? For Venat to step up with all this. "Oh and by the way. I'm the only one who knows anything about it."
They would treat her as if she were crazy. There was no proof of any of it and nothing TO prove any of it.

All she could give people is some whacked-out story about a time traveler coming back and relating events from the future, in which the world is sundered, practically every Ancient being is dead, a mind-wipe that conveniently leaves her as the only person who remembers.

You see how Emet reacted with the story in the MSQ, right? Utter garbage. It can't possibly be true. You think a majority of the Ancients would think differently?

Remember these are the people whom any number of willingly gave their lives for Zodiark to come into being. And then more still gave their lives trying to bring the first group back.

What many don't really seem to grasp is that the story is nothing more than a simple time loop.

1. We are born, a reincarnation of Azem.
2. Hydaelyn makes us the Warrior of Light.
3. ARR -> HW -> Sb -> ShB
4. We go back to Elpis.
5. We witness the cause of the Final Days, partially triggering it by our presence and the foreknowledge we give to Hythlodaeus, Emet Selch, and Venat. (This is why Hythlodaeus keeps calling us his "new old friend".)
6. The foreknowledge which enables Venat's memory to remain intact and thus allow her to become Hydaelyn.
7. We return to the future to continue the story. Hydaelyn moves forward through history to #1, and then she moves forward as well, to the point where we meet her in the Mothercrystal.

There was never an instant where we weren't on Elpis. The MSQ that took place there always happened historically. Just nobody knew it, because how could they? Even Emet-Selch didn't know, because his mind was wiped.

It doesnt sit right with me that were basically going there and acting all smiles and sunshine when we're talking to people we know are doomed and are doing nothing to stop it.

That's the thing though. History can't be changed. You want a good example of this? Watch Futurama, s07e03 "Decision 3012". If you've seen it, you have a good idea of what I'm gonna say.

1. Something bad happens.
2. You go back into the past and stop it from happening.
3. You succeed in stopping it.
4. It immediately happens anyways. Because by stopping it, you lost the reason for going back in time in the first place. IE, you never went back in time, so you never stopped it, and the bad thing happens anyways.

In XIV terms, you can't stop the Final Days, Zodiark, or Hydaelyn from taking place.
If we stop the Final Days in the past, the world isn't sundered, and we don't exist, in which case we can't go back in time, and the Final Days takes place anyway.
Just like you can't save the Ancients, because honestly who is going to believe you? You aren't seen as anything more than a familliar. And you and Venat are the only two who actually know what was going on.

The concern in MSQ about us changing the past, and not interacting (because we are incorporeal at first), was never really a concern. We didn't change anything by going back into the past. The WoL has always gone back into the past, the events on Elpis always played out that way. Our presence was necessary not to change the past, but to ensure it happened exactly as it was.

Of course, that's all because this is how the story was written, etc etc.

If you need another example, Back to the Future is a good one. The story makes like Marty was changing things, and he was, technically. He ensured that his mother actually noticed his father. The argument is the same as what happens in XIV. Marty always went back in time, and always helped his father and mother fall in love, thereby ensuring his own existence.