First, I concur that there is no "natural definition" of "natural". When
speaking of Chaos, what really matters is a THEOLOGICAL (in the broadest
sense) definition of "natural". Taking a page from some Orthodox
theologians, perhaps many cultures in Glorantha view "natural" from a
similar perspective: Regardless of the current state of affairs,
"natural" is the state in which things SHOULD have been, had chaos (sin)
never entered the world. What exists today is a result of the vestiges
of natural fighting against the weight of chaos (sin) that oppresses the
world. It doesn't have to be logically consistent. Theology ultimately
derives from revelation, or impression of revelation, when it disagrees
with "reason", it is "reason" that is to be discarded.
Of course, this is only if you want a theological or mystical Glorantha.