King had Queen by his side, and a boatload of fodders.
When Marco was laid at on his back and stated to have reached the limits of his stamina, King went to attack Zoro and Sanji from 2 feet away, and Marco intercepted him with ease.
Nobody disagrees that Marco fought King and Queen for a period of time. At a point, Queen went on to fight Chopper and then Sanji.
We then see King and Queen standing, Marco down and Sanji down. While we hear from Sanji that even though Queen was fighting him, King and Queen both participated in knocking him down.
Meaning King could beat Marco offscreen before he and Queen joined together to knock Sanji down as well. (And before you show your outrage, yes Marco was nerfed. I don't disagree with that.)
I still scale Marco over King when it comes to speed however the fact that he could beat him shows their speeds are comparable. And until Katakuri and Snakeman are proven to be faster than/can keep up with Marco, the person who kept up with Kizaru btw, it is only logical to scale both of them lower than Marco and King.
Nobody is saying King is gonna speed blitz Kat. I still think their speeds are comparable, King, who's main fighting style revolves around speed, is just faster.