Ok, I’ll bite, please demonstrate how Humphreys set up his equations so that he’s “right no matter what actually gets measured.”
It was a variable, for the fraction of dipoles aligned at creation. That fed into the magnetic field of the planet at creation, and that fed into the equation to predict what it will be.
The problem is he gets to set that variable for fraction of dipoles aligned to be whatever he wants, so he gets to have whatever result he wants.
And all this assumes the exponential decay idea has any merit, and it’s not on firm ground either.