Disappointed in one Endwalker Aspect [SPOILERS]

[Veloran]

It split the souls of every life on Etheirys, causing their lifespans to shortened by a multiple of the times they were divided. It also reduced their resistance to ailments by that amount. In real world terms, the average life expectancy is about 77 years for a person. If a real person were to be sundered, they would live for about 5 years and 7 months.

I don't think this is quite the case, given that if it worked on multiples than the Ancients would "only" have lived about 1400 years. Pretty long relative to the sundered, but a far cry from how they're presented and described throughout the story.

Granted we also don't know exactly how the sundering was performed. That is to say the order in which it happened. For example the Source being divided fourteen times to make the 14 shards would be quite different from all of the shards being created simultaneously out of fourteen evenly divided pieces of the Source. It could be the First is actually about half the density of the current 7/14ths divided Source if it was truly sundered first. Meanwhile maybe the Thirteenth is actually like 0.07 percent the density of the original world. Or alternatively maybe it happened a different way entirely.

there were imediately post-sundering civilizations, the Qitana Ravel cave paintings for example.

We have no idea when the Qitana Ravel paintings were created, only that it was before Ronka. It could be they were painted by someone with the Echo, or even that one of the Ascians aided in creating them (Emet is a "patron of the arts" and shows up there right on cue for example).

[Vyrerus]

I don't think this is quite the case

It's likely not. I'm quite aware that this portion of the story purposefully lacks specifics, because the specifics aren't the point and are harder to write/relate with. But it is illustrative of my point.