Too soft, any material with significant give will wrap around the apex no matter how flat you keep the blade. This in turn can create the scenario where you're happy with an edge, but just wanna give it that little extra bite so you strop it, only for it to feel a lot less aggressive, dull even. It's why a lot of the fixed angle sharpening systems use lapping film stuck on glass. That is if the goal is to get a mirror polished edge and keep it sharp, because you don't really need to go anywhere near that far to get hair popping sharp or worry about the material or "give" of the strop all that much if at all.