Zodiark's Codex entry what do we think about it?

[RyuDragnier]

Yeah we do. There was that NieR crossover short story.

Which tells us nothing. Here's the exerts from it, written out from the imgur screenshots.

Light triumphs with a sundering blow.
The powerful mage and his allies manage to withstand its impact. Barely.
When he opens his eyes...As the star lies shattered, so too do the souls upon it.

"Unnngh...Aaah..."
Pitiful moaning of malformed creatures...
They can no longer shape words. Language, culture, knowledge--forgotten.

Such an outcome is unbearable.
The man throws himself into restoring his star, his people...his paradise.

Decades...Centuries...Millenia pass.
As he works tirelessly, the wretched creatures begin to learn.
They speak in new tongues.
They worship new gods.
They forge new histories.

Nothing about that tells us anything about the time between the Sundering and the first Calamity. Supposedly the Twelve were around during that time, and we have no clue what they were doing either. 6.5 might tell us with the final 24-man's story, but until then, we know absolutely nothing.

[Lurina]

Which tells us nothing. Here's the exerts from it, written out from the imgur screenshots.

Nothing about that tells us anything about the time between the Sundering and the first Calamity. Supposedly the Twelve were around during that time, and we have no clue what they were doing either. 6.5 might tell us with the final 24-man's story, but until then, we know absolutely nothing.

Sorry, I missed this on the last page.

My point in bringing up the Nier short story is that it firmly establishes that mankind post-Sundering lost their cultural knowledge, though that's already inferrable from the text of Shadowbringers stating twice that they lost their memories and the fact that were reduced to making cave paintings. Actually, it was probably unnecessary to bring up the Nier stuff at all. All the rest of it, including this discussion on the meaning of "malformed creatures" and the state of their physical bodies, isn't even really relevant.

No cultural knowledge + no magic = hunter-gatherers.

Bringing up the 12 as stewards of the planet is a fair point, but even then they were only active on the Source, so for 13/14 people "created" post-Sundering they're not really relevant. That's not to say the game won't add more information and make the post-Sundering period come across differently, but with the information we have about the 0th Era we have at the moment, that's how it seems to me.