From the looks of it, King uses his fire to heal wounds, and he could just lol-heal something as lethal as Lion's Song; one of Zoro's strongest attacks outside of Asura, possibly top 3 after Asura and ISDS/SS.
As of now, King has:
-Defensive wings that have higher base durability than Dragon Kaido's scales
-A top tier instant regeneration ability. Likely only Marco has better one.
-High high tier CoA and AP, being able to overwhelm the Zoro who harmed Yonkos up top and momentarily blocked strongest attack in history.
-High high tier mobility and speed on top of flight. Is keeping up with Zoro's attack speed just fine, managed to easily catch RS Sanji, etc.
-Fire stuff, sword, ranged attacks, etc. A lot of versatility.
And he possibly (almost definitely) also has:
-Fucking ACoC. Or at the very least, CoC
-Awakening. Obviously... being the strongest non-yonko Zoan in canon so far.
Powerscaling King by the time he completely shows his arsenal... now that will be a trip. The fucked up part is that Katakuri/Luffy fans have wanked the ACoC/CoC/Awakening agenda so much, they have nothing to say.
I guess only argument left will be "m-MuH mArcO kIcK"