yuh , but one shouldn't determine king's superiority just from these 30 minutes ... taken the fact that he fought both king and queen simultaneously dozens of minutes whilst using his flames to cure people
Except it is not based on only that.
We know even before Queen vs Chopper, Queen was not focused on Marco. He was more focused on Hyogoro and Chopper.
Also after the 30 minutes, Sanji took over to fight Queen...minutes unknown.
And then we learn from the spoilers than Marco is Currently too tired.
It goes to show that it was predominantly caused by King since he was the one who mostly fought Marco.
However, this doesn't mean King > Marco because they didn't have a full fledged 1 v 1 but it does mean so far King and Marco are the same level signifying their yc1 status.