We literally just got confirmation last chapter that Kaidou and Big Mom had their haki active, whatever that means. Armament isn't reserved to hardening (kouka), that's one form of armament. Just because you don't see "hardening", does not mean armament is not being used.
As convoluted and asspullish as haki has been, that is one of the most basic and straightforward concepts to grasp, and you still seem to be struggling with it.