He is yet to master is acoc, acoa and even future sight. Thats his peak from df aspect not haki
Has it ever been said at some point that he doesn't master Acoc?
It was initially mentioned by Kaido that its usage was strange initially, but after Round 2, Kaido didn't mention it anymore.
About his FS, I think there is no more room for improvement, Luffy was using it perfectly well and in an extremely great way in his fight.
About peak of power, he didn't specify what he was referring to, but only stated that this is the peak of his power.