Well, we know that there was *something* before the gods.
The whole point of The Wheel is that it brings souls from across the planet to Ukaizo for processing, hence the presence of luminous adra only in the Deadfire region; it's full of soul energy. We know that adra is natural and it has some intrinsic relationship to soul energy, despite whatever meddling kith get up to. Remember the piece of living adra you stand on to talk to Eothas? It's grown over thousands of years towards the centre of The Wheel.
It's likely that when the Engwithans that became the gods ascended, they ceased to be the people that they were, and lost whatever memories that they had, perhaps purposefully, so that none of them would abuse their new powers and muck about with The Whee.... oops. This combined with the mass extinction of native life in Ukaizo/ The Deadfire immediately afterwards, and The Leaden Key's activities would ensure that knowledge was lost for good.
Also, the giant skeletons at the base of The Wheel with a few missing was an interesting detail, thoughts?