ZKK was a fun concept, but poorly evidenced theory. Nevertheless, I wanted it to happen after Kaidou was already defeated.
Luffy is not a killer, no matter how angry he is with someone, he always talks about beating them up, not murder. I didn't think it was appropriate for him to kill Kaidou, but Kaidou was not someone that could be let off with a beating. He was a problem that required a permanent solution.
Wano introduced the concept of "wings" and I found it thematically fitting for it reflect two simple truths: Sanji's first instinct is to protect against threats, Zoro's first instinct is to eliminate threats.
I wanted Zoro to be the one to put down a defeated Kaidou because imo he was the most suitable person on the Strawhats to kill for Luffy - not because he was ordered to, but because it had to be done and Luffy would never ask.
Some might point to Jinbe and his past as someone capable of killing an already defeated foe, but he was too new to the crew for that to work with him.