And they were not as powerfull as Luffy G4 from that moment.
King and Queen are in the league of Katakuri and Luffy barely won against him 1 month ago while Zoro and Sanji has no feats comparable nor have fights with people comparable to a monster like Kata. They don't even had any fights with characters like YC3, a guy who already was a problem for Luffy G4 start of WCI and above his version of DR which is above Doflamingo who is above Zoro/Sanji from that arc.
It's pretty delusional to think for a Zoro vs King and Sanji vs Queen or viceversa after seeing all that evidence.
Tag-team are the most logical way, and more in this atypical arc.
I can make some arguments too xD.
PS: ofc Oda can ignore all that and make a King vs Zoro and Queen vs Sanji.