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

[Lauront]

Exactly this. Dislike for Venat's choice to not tell anyone can be more productively focused on the awful Time Loop. Venat chooses not to tell people because she knows Fandaniel will be instrumental in developing the plan to summon Zodiark. She chooses to sunder the world because she knows the people of the future (namely you) will be able to rise up and defeat Meteion, instead of trying to go back to their "perfect world" where they forget sorrow or sadness or whatever.

The entire Elpis storyline falls apart because you can see the iron hand of the writers forcing it to fit into the Time Loop.

I'd agree that the focus should be on that, with the caveat that I wouldn't go as far as to say it absolves her, due to the fact that she says she'll take nothing for granted, and because Yoshi moots it as a possibility that she worked to actively preserve the timeline, thus I'd say her actions can still be questioned in their own right (and they do word it as a lot of it being based on her belief about things.) Where the time loop muddles things up is that it certainly gives the impression that she has a "fallback" option, meaning she could afford to give up on her people when they didn't respond the way she wanted (again, the rationale for the lack of concrete evidence presented to them is shaky due to other plot elements and her own "nothing is impossible" mentality, but certainly some do take the time loop as a plausible reason for it), and coupled with not subjecting her to the memory loss, they essentially place a lot of what is to follow directly into her hands.

I was surprised then they actually bit the bullet to do that, and it only exacerbates how dissonant her treatment within the story is. So it's a combination of a lot of things and it ends up coming across as really sloppy. There's ways they could've written her (e.g. subjecting her to the memory loss) that would've worked better and really, why involve a time loop when you have the Echo as a narrative device... unless the idea is to establish an AU. But they didn't. Unless there's one coming...

There's other issues with the time stuff as well, like the fact that things are just the way they are because you told her, rather than having an independent cause shown (as mentioned the unsundered escaping), and there's the potential for that to be abused further. Coupled with the fact that just one expansion before they showed an AU could form out of such time shenanigans, it made it that much worse to many, myself included.