Jojo - I am sure it has a significant effect but not enough to account for the thousandfold difference in wear rates.
I have also ridden in Peat / quartzite mud without massive pad wear - but under conditions that are not so cold. and with quicker descents where you get more heat into the brakes.
Just from attempting to make some sense out of all the data - its a puzzle that amuses me to investigate.
There are may factors involved but temperature of the friction surface seems to me to be the critical one. Composition of pad and mud has an effect for sure but some people get massive pad wear and some don't in the same conditions ( wet Afan / peaks etc) so there must be another critical factor.
Science officer did an analysis of this that gets as close to the right answer and as convincing an explanation as I have seen.