Nice call, but it also got me thinking.
Since Marco only managed to hurt King once with his knee attack and Zoro only managed to hurt King once so far, I wonder if King's durability has something to do with his race.
Like, what if, the Lunarians' wings are capable of memorizing damage they survived as long as the divine flame on their back is still burning. This is how King no sold an attack that even Kaido was unable to defend against, because he had his flames "memorized", for lack of better words, Zoro's swords attacks with that first Onigiri and now his wings can block any attack from Zoro.
I think this might play into King being a masochistic pervert according to Queen. As in, he is a M not only because he liked it, but because he self-harmed in hopes to adapt to more damages and gain durability. This might explain why none of Marco and Zoro's attacks worked on him after their initial hit.
And this might eventually require Zoro cutting down the divine flames to allow King to be defeated normally.