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

[Lauront]

Well Venat didn't think so, so she sundered the world to make them know suffering. As the previous Azem, she saw a lot more of the world than everyone else and was more likely to know.

On the point of suffering, even Venat does not deny that they knew it - her claim is solely that they were able to rid of it for a time:

Venat: No, it will not, for there has ever been sorrow. Mankind was but spared its biting sting for a time.

Again, the issue (in her eyes) is not that they were oblivious to it, but that she thought they weren't going to respond to the crisis the way she wanted, and wouldn't change, according to the Q&A. Not that they'd never experienced suffering. One can take it a step further and say the reports Meteion brought back validated her romanticisation of suffering and, when her kin weren't acting in line with her expectations, that sufficed for her to give up on them and try another route, by ending them...

It's not something I'd seriously argue, but my Headcanon (TM) has always been that Azem didn't really have a concretely righteous reason for opposing Zodiark - they simply could not, emotionally, handle doing that to Themis - even if they couldn't come up with any alternatives - and a meltdown accompanied by ditching the Convocation ensued. I like the idea both on a JUSTICE FOR THEMIS level and also, I'd rather avoid treating Azem by default as the moral arbiter of all that is good and right and so different from those terrible Ancients, etc - which is how a lot of people seemed to respond to that grape story on the Lodestone, lmao.

Indeed, I was dreading them doing something like that - I never read the story that way, as to me the real focus was to explain their relationships and show Azem had similar traits to their model WoL more than trying to demonise the other ancients, and it would be one of the most off-putting things they could do had they gone through with such a thing as you mention.