Thinking that Zoro can harm King even with the flame doesn't make you a fan, it makes you a good reader and an understanding person.
- Oda, the only man who is always right, gives you the same parallel about fearing being harmed by both Kaido and in this case it is more than confirmed that Luffy can harm Kaido, as well as King, so the most logical thing is to assume that King can be hurt by Zoro.
- Added to this is King's change of attitude, before it was all laughter, he didn't bother to dodge Zoro and after the KOH he suddenly dodges and defends himself. There must be a reason? And since Oda knows that there are some fans who have a hard time interpreting things, the previous comparison already gets you.
Right now, apart from cutting a Lunarian with the flame lit, the next toughest feat in this regard is wounding Kaido. If Zoro has the second most powerful feat in his possession and you still doubt that he can harm King, then I repeat that no one can except maybe Shanks.
Which means either no one is stronger than a YC1 or it means it's a bad argument.
That Luffy did not use the G5 against the Seraphines, there is no proof that he can hurt them with the G5, so irrelevant. Also, coincidentally, King never faced the flame of him with the KOH that AdvCoC has. And coincidentally, neither Luffy nor Zoro used AdvCoC against the Seraphines and lo and behold, they didn't do them any harm.
Don't you think it's a coincidence that King begins to defend himself and dodge the KOH, that at no time do we see the behavior of the flame against a KOH attack, and that neither Luffy nor Zoro use AdvCoC against the Seraphines?
Because I and many people, we see a lot of coincidence.