” magnetic field fluctuations are just a uniformitarian alibi for events”
Not “just”.
I’m sure they can be! And that there are examples of the backward doing so. But radiation-caused mutation is an established fact. And a huge weakening of the magnetospere would increase mutation.
A strict limit though would be “beneficial” mutations. Very rare. That’s the catch.
I don’t mean to denigrate the study of mating-influenced genetic change, and the myriad factors involved such as climate.
But it’s a fact that radiation can cause it too.
( Though beneficial mutation is a rare result in all but the simplest organisms- it happens.)