Sen-chan... Impressive how fast you jump onto the wrong road...
There was no fire and he was focused on movement speed during Imperial Archer when Zoro attacked him with Ultora Gari and what happened? Nothing. There is no gimmick.
Marco has hit King while he had flames up, there is no "failed to activate defense in time" thing...
Every combatant tries to hit weak spots, it is not a Katakuri thing, lol... There is no weakness though...
Really funny how you make stuff up that doesnt exist...