Where is this stated? I could see things happening this way, but it there any information in the game supporting this version of events? Iovara certainly doesn't say that she learned about "the plans", and it seems the gods were already there at the time of her death as her soul got stuck at the Court of the Penitents.
Everything from the flashbacks indicated that the Engwithians were still a functional, thriving civilization during the Iovara parts. And as far as I know, Thaos was the only survivor of the Engwithians.