In my firefighting days (mid-1970s to mid-1980s), I always wore Danner Smokejumpers. I usually didn’t get them resoled, though, because one good season would generally ruin the uppers. Heat is, indeed, hell on boots. It wasn’t just the Danners, either; those who wore expensive Whites and the like didn’t seem to get any more life out of a pair.
Most of my firefighting is burn piles. In addition to tree tops, I burn about 10-12 cords per year of split oak in piles to make charcoal for incorporation into soil. That gets my boots so hot it sometimes melts the laces (I wear an aluminized nomex suit). Even then, I can usually get two years with one resoling. Lately, I've bought cheapo boots (Dickies) for weeding, mud, and fires and saved the Wescos for logging and high climbing. They have a Cambrel (kevlar) lining to protect from saw cuts, so they aren't terribly comfortable.