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

[Rulakir]

The most boring thing they could've done would be to make Zodiark or Hydaelyn the big bad, which they didn't.

Except Hydaelyn is still the antagonist to the Ancients, even moreso now given what we learned in EW. I didn't clarify this enough in my initial response as to why I felt like the narrative was gaslighting me. Her actions align more with the villains, in fact she shares numerous similarities to Hermes, but the storyline treats her as the opposite. Even saying she's the heroine of the WoL's tale is being generous since our reality is a direct result of the decisions she made, choices which led to the deaths of billions and wasn't guaranteed to save anyone.

Again, it wasn't a gamble when you know the outcome.

This is a problem because it means she knowingly sundered additional reflections for the purpose of serving as fodder to the Ascians who would rejoin them. So, if they were morally reprehensible, then so is Venat if she were purposefully trying to recreate the events that would lead to the WoL.

Should you choose not to believe that, then we have the Crystal Exarch's timeline, which Veloran in the lore forums noted, is the antithesis of the messaging of EW. They refused to accept their fate after the 8th Umbral Calamity (which was tame compared to the Final Days), labored for 200 years to undo it, and sent G'raha back in time under the belief that in doing so they would all cease to exist. His timeline is the complete failure of everything Venat sought to achieve to the extent that the 'superior' sundered, as we're led to believe, ended up being no different than their unsundered ancestors when push came to shove.

[Imperius_Relampago]

This is a problem because it means she knowingly sundered additional reflections for the purpose of serving as fodder to the Ascians who would rejoin them. So, if they were morally reprehensible, then so is Venat if she were purposefully trying to recreate the events that would lead to the WoL.

That is correct, however Venat and the Ascians had one major difference. The Ascians saw Humanity as inferior shells of what they once were, and saw us a gnats who should be stamped out. Venat truly loved Humanity, and was in pain as she watched Humanity suffer through the rejoinings. Rewatch "Cutscene #2 of the "Thou Must Live, Die and Know" quest cutscene, and pay attention to the songs lyrics as they spoken, as well as the visuals in the cutscene. Venat/Hydaelyn became more bloody, damaged and tired as time went one. This represented her watching Humanity suffer as she walked past them, ignoring their cries for help. The song playing in the background, "Answers" is a combination of Ancients, Humanity and Hydaelyn singing. The deep male voices are the Ancients during the Final Days, as they despaired and desperately hoped for Zodiark to save them, constantly calling out to the star asking "Why must we suffer?", with Hydaelyn responding "walk free". Then it cuts to Humanity being beaten with every Rejoining, echoing the cries of the ancients, but with a female voice "Why must we suffer so?", along with "Now open your eyes now that our plight is repeated", "Still deaf to our cries", and all of Hydaelyn's responses are apologetic. Near the end of the song, the Ancients and Humanity sing together (symbolising the WoL carrying the Ancients legacy, as well as the hope of Humanity), with Hydaelyn giving her famous "Hear, Feel, Think" lines inbetween them.