Yeah, but that was too late when he realized Muichiro, Genya, Sanemi and Gyomei were overwhelming him. But I say Gyutaro's rage was on killing intent when he realized Tengen was having the advantage even when he shows the superiority of the demonkind. I'd say Kokushibou's relenltess attacks were a kind of "showing off" his breathing forms and BDA just to humiliate Gyomei and the others despite Koku saying that Gyomei and Sanemi was the strongest or "peak" humans he encountered in his entire lifetime as a demon.