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

[Causante]

I would agree that the tempering was limited to the Convocation and anyone else who may have been immediately present with the summoning. But the Convocation making decisions others didn't believe in did have an effect on the populace because while Venat and everyone else were A-OK with summonings 1 and 2, the 3rd was what caused the main debate and ultimately the Sundering.

I don't think people didn't believe the convocation, their decisions saved the remaining ancients and restored the planet albeit at a terrible cost and people had to volunteer for that even before the summoning ocurred after all. Your conclusion makes it sound like zodiark was manipulating the convocation, which in turn was manipulating the populace, prompting venat to perform a drastic act to save "life". I'm sure you'll agree that's not what happened or how it was portrayed in recent expansions.

Tempering also has seen to have had some degree of control over the Ascians as well, unless you want to fully retcon ARR and say that all the scenes of the Ascians deranged praying to the "one true god" didn't happen.

I'm pretty sure we're supposed to accept that as full retcon. I may be wrong on this, but I don't remember ascians praising zodiark as a "true god" in a fanatical sense since they changed the writing around the ascians. What it felt to me is that from then on they treated zodiark as the embodiment of their hopes for a future where they could recover what they had lost.

In my mind this makes sense even in a logical society if you think about it. They were on the verge of extinction, everything they knew was being destroyed and people around them dying. All this happening without a cause or a reason (from their perspective). And then this all powerful being makes everything stop and is even able to restore the planet (to some extent) to what it once was. I think it should be doable to understand that a lot of people, specially those less versed in the sciences or creation magicks, would start to worship their "savior". Others, on the other hand, would be afraid of him given what they had (as a collective) to sacrifice, which would explain why they were so divided. The mental state of the ancient society must have been chaotic after dealing with such a catastrophe.

This scenario could've been explored way better to try and give more convincing explanations for the downfall of ancient society and Venat actions, but it's not how they went about it endwalker. It's not about Zodiark, it's about Hermes and Venat's beliefs.