Killer vs Zoro
Apoo vs Zoro
King vs Zoro
Zoro's attack on Apoo isn't even debatable; an ittoryu style attack, without hardening, one shot him like nothing.
Against Killer, Zoro put more efforts to one shot him but given the fact that he neither wielded Shusui nor Enma, his AP was even nerfed. He used Onigiri with hardening on him.
But on King, this is basically post Enma-training Zoro, wielding Enma, wielding his bandana, using Onigiri with hardening on King's NECK, yet the same character will struggle off a powerful move like that.
Whatever people say, I think this clearly shows the gap between King and Killer, let alone Apoo who was fodderized.