There really isn't so much a difference between King and Queen, the same way as Zoro and Sanji are seperated by a margin. To the point that it would be a tossup still rather than an outright defeat if the opponents switched. There is no point of rivalry between both sets of characters if they were not comparable. Oda throughout the series made this clear.
Sure Zoro is slightly above Sanji, but not to the point that Sanji would clearly lose to Zoro's opponents.
People keep quoting King's beak dive on Sanji, but the same dude was throwing Zoro around Onigashima. More a testament of King's ruthless no games fighting style than anything. A better matchup fighting style and persona and plot, as the characters clearly are made to be counterpoints to the wings of the pirate king.