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

[Brinne]

And also think about it, Venat's supporters wouldve had to know that the plan was to sunder since that wouldve been the plan to create the Hydaelyn primal. Both sides knew the risks of their plans.

We don't know that! IIRC, they were aware the plan was the Sunder Zodiark because they were aware that the world still required his protection, but they didn't want him to be an active influence upon it, either. It's still ambiguous if they were aware that Sundering the entire world itself and every life upon it was also part of the package. What Venat's short story highlights, however, is that she made the deliberate decision to tell others as little as possible about what she knew. With that in mind, while both sides knew there were "risks," saying that there was equivalent knowledge of both sides of the risks when Venat had direct knowledge of the future and what would happen in both the Final Days and the Hydaelyn vs Zodiark conflict - whereas the rest of Ancient society was flying entirely blind and scrambling to do whatever they could without understanding why it was happening - does not really ring true.

As far as the rest of your post, I've always held that while I have my own subjective opinions on the exact nuances of the conflict and the people involved (Venat's logic is a bit more moon logic to me as an individual than the Ascians', though I don't question that she genuinely believed what she did), I'm more than happy to agree to a common ground in general that the Ascians and Hydaelyn can be understood to be roughly morally equivalent to each other. Both committed absolutely heinous atrocities and were willing to sacrifice untold amounts of unwilling victims for their own visions of the greater good, for the sake of the world.

Also, I apologize, but I'm having genuine trouble parsing what you're saying about the self-sacrifice...?