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

[Lauront]

There's many ways they could've broached it that would've left her as more sympathetic. My favoured approach was for the instigator of the Final Days to stoke the conflict between the factions to rid of Zodiark as the obstacle to their plans by fomenting a course of action by the Convocation that would concern those paranoid of Zodiark's power, only for the enervation aspect to work unpredictably and result in the Sundering.

The game did a very awkward take with the a world of suffering is better than a world without as people might get bored with out suffering

TBH I don't think they even made that point. It's more a message that you need a mixture of both, because the first two worlds, while they annihilated a specific issue, nonetheless were pretty dystopian in other respects, and seem characterised by immense suffering. Meanwhile, by all accounts the dragons had a more or less blissful star but it was subjected to senseless destruction outside of their own control and on a scale they could not come back from without fleeing it. Senseless destruction that no hopium could undo. I think the game is very poorly and awkwardly trying to make the point of being able to maintain hope even in the face of extreme despair (as the answer to Hermes's own nihilistic mentality), but where it fails IMO is trying to brush aside any and all collective attempts at formulating a purpose, in showing e.g. Y'shtola just brushing aside a problem the Ea faced - not that she'd ever run up against it in a meaningful way. The ancients themselves broadly fell under the umbrella of societies with a collective purpose, but nonetheless retained their own individual goals. On the other end of the spectrum you had Zenos; his goal is self-authored, but for all the strength he has, it ends up meaning very little in the end as he is a husk of an individual, so it's clear that individualistic formulation of a purpose can also be taken too far and become empty.

Nonetheless, none of that would suffice on its own to condemn the ancients, because they resolved to save their star and sacrificed to do so by bringing into being Zodiark, to both shield and restore the star. All the nonsense about time travel and the Plenty is required, in my view, because the ancients had yet to succumb to the fate of the Plenty, and given their inherent love for their star, would likely adjust as necessary if they knew of this issue and the threat it posed to them as a civilisation. Thus the time travel gives Venat a potential roadmap with which she can damn her people for not responding to her liking in terms of avoiding the fate of the world described in a few lines from Meteion's report, and not be painted outright as a villain. Although I think the recent Q&A puts that in a rather more questionable position.