King is strong and has some "bullshit" with his race, on top of being an ancient zoan, but I think that mainly just puts him on level playing field with other top commanders, who also have bullshit, like Marco with his regeneration and Katakuri with his FS.
I think you could probably make an argument for King outlasting both Marco and Katakuri in a fight due to how tough he is, as well as the fact he doesn't seem to be losing stamina like Marco was, and Katakuri is someone who is noted to have his FS weaken if he fought for an extended period of time.