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

[linayar]

Emet-Selch mentions that memories of the sundered were fragmented and unable to recall specifics of anything.

It's not really made clear exactly how badly mankind regressed in-game, but the lorebook mentions that creation of stone tools and the discovery of fire were among the defining attributes of the "age of gods" which suggests they were in an extremely primitive state.

I have a hunch that the Twelve were part of a post-Sundering contingency plan from Hydaelyn to ensure mankind could actually get back on their feet and recover instead of simply going extinct in the face of their newfound shortcomings.

I think that has to do with the loss of creation magic, which of course would be a big deal.

In fact, creation magic is such a big difference that it became a crutch for their society and why they wanted to return to that prior state when their magic was not being turned against them.

Okay….then you should agree what Venat did was Genocide. The ancient lives were no more, she even says herself she is the last of her kind. She ripped them apart, and then removed as much of their history as she could and kept it all secret. Even if we don’t count the ancient lives themselves, she introduced much shorter lifespans and sickness to living beings, all those deaths are on her hands, which is indeed genocide. Not to mention her backup plan in case we failed was also allowing the shards to all be killed.

I agree that the resulting situation is worse, but I don't agree with genocide. Venat calling herself the last of her kind refers to being unsundered, but that doesn't change the fact that she still sees the sundered as continuation of mankind.

It does not, but this one sure did!

Well, that's the point of contention.

No. He confirms it in the cave scene where he reveals Hydaelyn and Zodiark are primals. "And the worst part? No one could remember it." Elidibus also talks later, on the moon, on how all knowledge and memory of the Ancients being wiped from history without a trace was Hydaelyn's intent.

Actually, that cave showed that they remembered and recorded it. Being wiped from history means no record was kept, not that the people who experienced it first hand had their memories wiped.