You're clearly being dishonest if you don't acknowledge the fact that Marco spent a lot of fuel on things other than King. Things Marco did so far:
-Travelled from whichever island he lives on to Wano via flight. Most people ignore this but I am sure he lost some of his stamina.
-Fought BM for an unspecified amount of time.
-Took hits from fodders. They still count even if they're insignificant.
-Took a few bullets from Queen.
-Fought King and Queen for a short period of time
-Fought King for around 2 or more hours in a one-on-one.
-Helped in slowing down the Ice Oni transformation.
It's clear as day he lost most of his stamina to Ice Oni and King, but the other things put together have a significant impact on him as well. All things considered, Marco is pretty close to King but King is definitely stronger.