What decks will really dedicate space in there deck for Heatmor? Any deck that does also have to play a good amount of {R} / Prism / Rainbow energy to not be screwed over by Lost Remover/Crushing hammer, which is alot of space to sacrifice for a low tier deck (but a decent deck nonetheless). The only deck i can realistically see teching Heatmor is CMT due to the {P} resistance forcing you to drop more energy onto Mewtwo EX, plus going aggro Tornadus is difficult when Hurricane constantly moves energy off of itself and it can be hard to maintain it for an entire game. That being said, you could argue Ruins of Alph removes the {P} resistance, but some Durant lists use Skyarrow Bridge, so that could cause problems.
Durant isn't a huge enough threat for people to get worried about and tech a Heatmor for "safety". Talk about your hard-counters though.