I mean, everytime King has shown hybrid form before, it has been without the flames while the opposite in base and Zoan forms.
The spoilers said Zoro observed that King trades durability for speed by putting out his flames. We still don't know the true mechanics behind the gimmick if we're being real.
I guess you can make the argument that Marco's fires dont do that based on him clashing with King in chapter 1022, that's entirely debatable i guess.
Regarding your theory, it sounds good but let's see though. We were given zero information about what happened combat wise this chapter - outside of the named attacks which were used. I guess when we get the long summary it would make sense. I definitely think Zoro cut King down in his most durable form, since it shows that he used a new move entirely - possibly coated in CoC.
I guess you have a point here.
Are there not instances when base/Zoan King didn't have fire on his back either? At least that's what I recall, I could be wrong about this one tho.
At the end, Marco's attack didn't do much - since King had fire on his back which pushed his durability. I always wondered how King tanked Marco's fire attack but bleed from his knee. Perhaps this chapter will give the reason.
In the beginning, I was also quite salty when writing posts in this thread but now that I have a much calmer look at this, I agree with your take that we have to look for further information. As people mentioned, Lance wouldn't give this chapter a 200/10 only because of King's face reveal I guess. I still hope we might see a COC clash or the battle continues (which I'll keep my expectations rather low tho). It also depends if King was on Full Zoan mode at the end as well.