My head canon has always been that Ula, Cosi, and Emeria are amalgamations of both the Eldrazi and the pre mending Planeswalkers that sealed them on Zendikar.
Yes. Three Cthulhu-type elder gods were sealed away by three (basically) demigods, then misremembered in humanoid form as regular deities. That statue shows the three deities but echoes the elder gods. New idea here is that the demigods influenced how that memory was shaped.
How are these stories told? In the game cards? Are they just for fun or do they they materially impact game play? Like needing both the demigod and statue cards to do something?
In bits and pieces on the cards via art and lore text, and then (at the time) in web fiction ("the story"). I wrote about this statue in a piece implying that stories about the trickster god Cosi actually encoded knowledge that the gods were false.
That lore is expressed in the game play, too. I chose to put the statue art on the card I did because that card helps you cast the elder god things and their minions.