Nice. I think we're all in agreement here that King's secret resides on the flames on his back. It's reasonable to think now if it were to be snuffed out, King's lifeline would be lost.
If our opinion is correct, this explains why Kaido took King with him to the Marineford. Of everybody present in MF, only Aokiji would be able to snuff out the flames. And, among the Shichibukais, maybe only Mihawk, since I doubt Zoro can slice off intangible things but Mihawk could not. Kizaru's lasers isn't going to snuff out his flames and Akainu's magma would just make the flames bigger. We don't have any indication that Garp and Sengoku know how to cut flames. In theory, he could virtually no sell almost every attack and would have greatly bolstered Kaido's campaign (had it not been for Shanks, who could likely cut flames, too).
And you're all correct that it's good timing that Zoro recently learnt how to cut fire. This makes it clear why King was able to easily defeat Cook and Marco together, because they could neither snuff out nor damage his flames. So he was able to easily no sell everything they threw at him and responded brutally. I don't know what is up with Enma and the Shamisen, but after Zoro gets his shit together, he should try Homurasaki on King. :cheers:
P. S.
I feel that all the Zoro downplayers who claimed Zoro is below YC1 level because he can't hurt King ejaculated prematurely (as usual). They attributed the whole thing to Zoro supposedly being weak instead of King having a cheat defense code.