While luffy was training in Udon, he explicitly says his level of armament haki was literally too insufficient to damage kaido… Then when Hyogoro qsks him what he wants to learn Luffy remembers Rayleigh, Sentomaru and the Boa sisters using an advanced form of haki… Then Hyogoro demonstrates the haki infront of Luffy and Luffy says yes, thats ehat he wants to learn
This is advanved armament haki…
Also, this is what both Kaido and luffy said later in Onisgashima is still too weak… Advanced armament can damage Kaido but its still too weak to reallt severelt damage him… As admitted by both Luffy and kaido…
Yeah, that's also advanced armament for me, but simply the brawler application or the application you by default have to use if you are not wielding a weapon, cause there is nothing you can put that "body flown off"- haki onto other than shoot it out in a barrier like haki blast.
But anyway even its superior form wasn't able to do much against Kaido, so it's questionable if barrier haki- as the actual barrier haki tech- would have even the slightest effect on him, as it is by nature still blunt force damage, same shit that could beforehand not damage Kaido aswell, even with tremendous power as Boundman's behind it.
I mean don't get me wrong, it's for me the same technique that makes users put haki on a sword, it's just that on a sword you've boosted penetration ability, cause of the nature of the attack type and which that haki boosted power you are becoming able to penetrate even Kaido's skin.
Which makes it interesting to me that you believe that Oden scarred kaido WITHOUT even using advanced armament… Yet Luffy and kaido say Advanced Armament cant reallt do shit… So what is Oden’s haki that it can scar kaido?
Like I said above, it's advanced CoA usage, as you need to be able to make your haki flow, then let if flow off your body and then put it onto your blade. And when Oden hakifies his swords, he's exactly doing that, which maximizes the sword's potency.
Advanced CoA again is just a technique/control based ability, the haki that's used is the same as always, it's just a way to use your haki in more advanced ways, as in putting it onto a sword or shooting it out in a pretty powerful haki blast.
They all are advanced haki users, but they are simply not making use of the "internal destruction" application, which they btw do not even need in the first place, cause they are already able to damage him by penetrating his super tough skin.