King doesnt have two gimmicks : healing flames and better dura/ better speed with or without fire.
When king is tanking tatsumaki with his wings, a feat Zoro couldn't understand, his fire was burn hot on his back. So his durability was at the best. And King even made a comment about how special he is.
Except if you think that he flame healed from that Tatsumaki too no ?
It's not or : He survived the SSSSS because the fire was on his back so that boosted his durability. There was no healing gimmick involved.
He can regen with Zoan and boost his durability with his race. That is already fucking good.