@Kaido:
Mihawk was introduced as the greatest swordsman of all time, so for him to use Haoshoku instead of swordplay would have been highly inappropriate. Plus, giving a nuance to his swordsmanship right upon his introduction would have made things unnecessarily complicated because the point was to show just how far behind Zoro was even without Haki, since he couldn't even cut steel. And so many other people used Buso in the war that Mihawk using it wasn't really necessary, especially since his only challenging opponent was Vista and their battle was put to the side.
Him showing up and being scary enough that people just fainted around him would have been fine. It was fine when Shanks did it on Whitebeard's ship without real explanation. (It was just described as letting out his spirit at the time, which was easy to grasp, even before official terms fell into place.)
The point is, Shanks, Mihawk, both showed up several times along the way and could have given hints of what an overwhelming presence could do to people. It didn't have to be spelled out or used to its full, just a hint that "these guys are so strong, weak willed men get wobbly just from being around them." WHich is dramatic and works fine and probably should have happened around all the Warlords to some degree. When Doflamingo and Kuma walked through town and were first introduced they could have given off dramatic fainting aura. It seems reeeeeeally out of place that the other top tier guys didn't know or use the abilities when fighting luffy, when every single marine vice admiral knows how. Enel had mantra, but he could have had some of the intimiation. Lucchi absolutely should have had some of it. (several of the CP9 forms are all made more awkard by haki existing, in fact.)
Oda had 15 years to fit in scenes of strong top tier guys using even a hint of some of the powers, and he never really did until it all started coming together around Sabondy. Rayleigh should not have been our first real example of making peons faint.
It absolutely should not have been "something that Hancock does that's unique to the kuja" like it was kind of presented as at first. The idea that only Hancock, Mihawk and Dofla have it? Is absurd.
It was fine that that's the point Oda started really explaining it, but he didn't have it solidly mapped out early on, or there would have been some other signs or scenes along the way showcasing it.