Zoro was using aCoc because he was releasing all his haki for the King of Hell style, remember that he had a time limit, you can’t release all your haki without a repercussion. Now he is aware of his Coc, he can use aCoc when he need it without losing too much stamina
Three sword style with Acoc/ CoA
King of Hell style ACoc+ACoa when he goes all out
For the Holy Knight Three sword style with ACoc is sufficient
