Disappointed in one Endwalker Aspect [SPOILERS]

[MikkoAkure]

Are we shown how long everyone lives on each shard or that their measurements of time are the same? No. This is a case of the scriptwriters presenting a plot fact, but then not showing or writing what it really means into the story, because that would be too difficult to really show. Keep in mind every shard is locked away from the real universe by a space-time dimensional barrier that only allows aether, and perhaps Dynamis, to pass through it.

If your theory was correct, then it would be a noticeable fact throughout history that people gain longer lives after each Calamity but there’s nothing at all to suggest that. That would be like saying that people died of old age before their 10th birthday immediately following the Sundering and that’s just silly.

Also, there are Viis who themselves say are over 100 years old on the First. If they were a fraction of the Viera of the Source then they wouldn’t live that long. We’re also shown that measurements of time are the same. The Scions all reflect on the years they spent there. You would think that some of the brightest people from a different world would be aware of time being different or a year being a fraction as short. We’re also given ages of a couple of characters from the First in comparison to those from the Source and not only do they look that age, they look like the same age as the characters from the Source.

If that was an actual possible theory, then there would be clues somewhere, but there’s not. It’s not even a matter of “difficulty”, there’s no point in writing supporting information for something that doesn’t exist. I’d need actual proof, not “my theory is so difficult for the writers to put in the game that they didn’t”.

I had to go back and look at the scene to see it. Y'shtola says, "it may predate the empire." because it's, "Unlike anything she's ever seen." Emet-selch merely says that anyone pre-Sundering would remember it. I said it was the Ronkans, due to the later questline where we see the Meteorshower Mural with the Vieran Sorceress.

The whole point of Y’shtola saying that the cave paintings predate the empire is because the materials used are “older”. You’re twisting the source material and quoted it wrong. The full quote:
Y’shtola: “The murals. If I am not mistaken, they predate the empire.”
Minfilia (Ryne): “How can you tell?”
Y’shtola: “A peculiarity of the paint. Most are made from mineral-based pigments, but whatever was used here is older than anything I have ever seen.”

And by the way, the Viis sorceress Tiuna had the Echo. That’s why she saw the meteor shower and why it’s in her mural. At least to me, the murals don’t look the same either. Different art styles. And one is painted in a cavern wall that was eventually developed into a shrine devoted to “the wisdom of the ancients”, the other is a mural painted on the walls of a ruin itself.