What exactly is going on with the Xaela's civilization?

[Lurina]

With hindsight from ShB and EW, Xaela mythology is weirdly accurate compared to other cultures. Their creation myth is the only one on the Source which specifically describes the Hydaelyn vs. Zodiark factional conflict (they even get Venat's former title right, despite the genders being backwards) with the two clans of Au Ra identified by which side they were on. They're also the only group we see that has mythologically preserved (as opposed to scientifically re-discovered) reincarnation as the accurate form of the settings afterlife. And Temelun, the chieftess of the Mol, displays a weird understanding of what's going on with the big-picture plot whenever you visit her at varying points in the story.

If you look closely at the landscape of the Azim Steppe, it's obvious it used to play host to a much more advanced civilization. The Dawn Throne seems like it's only the top of what was originally a massive superstructure; we only see the fingers of the giant sculpture surrounding it protruding from the ground, while going underwater seems to reveal it's just the top of a buried tower. And of course the Dusk Throne is almost completely underground.

So what do you think is up with them, specifically? Ishikawa wrote the Azim Steppe content herself right before Shadowbringers, so it's hard to believe she didn't have anything in mind.