Cool not the point. Invisible armament haki is the weakest form of it. So the notion of kaido and bgmom being yonko is also mute.
It's an example of a person using Invisible armament to nullify a fruit ability. This was also shown with the tashigi and smoker vs law fight. Law cut tashigi while smoker was warning her that her haki wasn't strong enough to even handle being in laws room.