That Sanji was a bandit with as many spotlights as Zoro in the capital
Kamazou managed to lose his weapon to Zoro (as a noob), due to not using gauntlets, so Killer was unarmed, and Zoro with 3 weapons. So it was easy for Zoro to finish it
''Kamazou didn't react to Zoro's attack'' is a lie, you can see that Zoro cut the scythe that Kamazou used, it means that Killer reacted to the attack, only that his weapon was too weak to defend.
The manga portrayed Zoro: rengoku oni giri = Killer: Zanshu Claw.
If you think '' Zoro is much stronger than Killer '' then you are stuck in your preconceived concepts, because that is not what the manga is trying to say, much less portraying.
Zoro high / extreme diff Killer is the best we can conceive so far.