Yeah, that's what baffles me. Why do people think that you can hurt king ONLY with CoC haki!? That's bullshit!!! Zoro himself (as far as I remember, I don't really read the chapters, only spoiler) had to wait for King to turn off his defense mode to actually damage him. Plus, Zoro's allegedly ACoC is vague as fuck, it's unclear whether he has the advanced version or just Enma magic imho.