Same here, have had several pairs of Muck, the heels would eventually wear out.  Tried a pair of Dryshod and the heel wore out even faster.  Just as warm but I really think the Muck were more comfortable.

I have glued a piece of leather over the worn spot in the heel and that last longer than the original material but its a pain to get to it and glue it so that it stays.  Both companies need to address that.