I don't understand the impulse to blindly accept the lore as 100% historically accurate, even in terms of the game world.
I don't understand either. Who are these people?
The purpose of reading the untrustworthy lore is learning what to doubt and what to correlate.
I'm sure there are some philosophical Imperials or Bretons who speculate more natural causes.
Those philosophical Imperials and Bretons would be complete dunces. Or, if you prefer, erudite flat-earthers. Because their only evidence is an a priori assumption from a different universe. Myths are natural and the natural is a result of myth. The existence of any fact, being, or phenomenon that does not have a magical precedent and origin is an aberration.
Nirn still has natural laws and scientific truths just like Earth. We just know their origin and some of the basic mechanics, unlike in real life. Myth is science, and I don't get why it makes people so uncomfortable. The whole genre of fantasy relies on myth becoming true. What do you think those centaurs are doing in D&D? ES just deconstructs the idea a little bit. It's a pity that the current taste seems to be for a world populated by ethnic stereotypes with a Monty Python and the Holy Grail backdrop.