Stop these mental gymnastics and notion that everyone hates Sanji when they don' put him over someone.
I cried and said Sanji wouldn't fight King and Queen simultaneously? I said it and it was correct, he didn't fight them simultaneously unless you are special and imagined your own version of One Piece. Sanji fought only Queen solo. The encounter with King before wasn't a fight it was a brief skirmish which King won at that time.
Anyone with eyes understand the logic behind Oda's writing.
Kuzan as well as rest of the Admirals are endgame material, Sanji is not going to beat someone as strong as an Admiral with how poorly his character is written, he's just going to get adjusted to his next fight and that's it. He has no fighting ambition and wants to see All Blue an cook for people.
He fights because the plot demands it. If Straw Hats fight Marines then he will fight Smoker who will be adjusted to Sanji no matter if you like it or not. We know Smoker is weaker but he will get adjusted to Sanji because that's who Sanji will fight.
Only Zoro and Luffy will fight Admirals and even that might be unlikely, Zoro will be lucky to fight Fujitora or Kizaru.