That is also true for the HD rain suit. I have a hole in my pant leg from where it hit the exhaust.
According to HD, pack lite gears are hear RESISTANCE (?!?!?), I guess it means occasional touch of the pipe should be OK.
I have a pair of pants from Eastern Mountain (Gore-Tex) very very nice and lite. My left leg touched the pipe on the old RK many times and no problem. One day I tried to get something out of the bag on the opposite site and chit, I got a 2" hole on top of my left thigh. What I like about it is full leg zipper, elastic at the bottom, flap over the zipper that has about 1" of Velcro every 8"-10". Very easy on/off.
I hate sweating in rain gears.

Interesting that when I search google for heat resistance rain gear, I comes up with HD links more than anything else.