Cero's are incredibly powerful, you still fail to realize any of this. Not only that, but regardless you can't even break Kenpachi's skin without a completely focused attack that's not only sharp enough to stand against his unconscious release of reiatsu and powerful enough to overcome it. You must've also been unaware that the Soul Society is not like Earth. Effectively SS is more durable, which is why, again, Shinigami are restricted in the Living World because they could wreck everything. Hell Ichigo's father even explained that powerful Shinigami have to control their zanpakutou, since their size can corespond to the Shinigami's level of power. Thus, as shown with the Arrancar Big Fisher, without controlling the size and form of their weapon, all captains and even some lieutenants would be swinging swords the size of skyscrapers.
Make a note, also. Kenpachi pierced the heavens and shook the ground, affecting the atmosphere with but one move; taking off his eye patch. I've already shown and proven that Mihawk lacks the ability to even hurt Kenpachi. And, even if you say he could cut Kenpachi, it makes no difference. Kenpachi can easily take every blow Mihawk dishes out without a care because none of them are any real threat to him. His durability and damage soak is insane. Even when impaled through the chest by Tousen, Kenpachi didn't even seem to even notice or care. Even Nnoitra stabbing him in the chest and punching a hole through Kenpachi didn't even remotely slow him down. Any cut Mihawk could even remotely make would be shallow and pointless. Nicks and scratches, nothing more.