Marco is the first division commander Vista is the fifth.. Of course they know haki and are pretty good in it. Since Marco made kuzan(aokiji) fly away by a kick and also kizaru flew away. So why did akainu just regenerate after the double attack
Maybe magma works differently? ... I think that, when I first saw/read the fight with WB and Sakainu, I saw Akainu's head bending a little, kind of like he did when Marco and Vista attacked him... So perhaps it's his DF different?
His haki overpowered there's and let him still use his df ability. Kinda like luffy in gear fourth doffy kicks him, but luffys body still bends like rubber and keeps the hardness of haki. Because use ing gear 4th luffys haki was better than doffys.
You can use haki to retain your DF ability - when Doflamingo attacked Luffy in Gear 4th, even though Doflamingo was using haki, Luffy's body stretched at the point of impact. Sakazuki did the same thing.
I think Akainu used Advanced Kenbunshoku and liquidified himself like how Katakuri did. As you could see Akainu was calm so he was able of doing it, render a kick or a sword slash, haki or not ,useless.