I still think King feels all the pain from when attacks hit him with his flame on, they just don’t actually damage him. So what King was doing here was just avoiding being hurt since he can’t be damaged anyways.
The complete invulnerability just makes 0 sense
Then why did he just give Zoro free shots to get stabbed? Why would he just blow himself up?
Clearly, if pain without damage was an issue for King, these wouldn't be happening.
King didn't even register Zoro as a threat pre KoH. He was just an opponent he can have fun fighting with.
This changed only after KoH.
The obvious logical conclusion that can be drawn from here is that KoH Zoro could damage King. It isn't just pain, pain comes from damage by the way anyway (King can't regen).