I think this primarily comes from fans not understanding Sanji's role. Zoro and Sanji are the wings, but it's better to look at them as the sword and the shield.
Zoro is the sword of Luffy, and usually his role is to fight alongside his captain, and to protect Luffy when he is unable to fight. Zoro has a will comparable to Luffy and is often times actually fighting on par with his captain.
Sanji is the shield of Luffy, and usually his role is to protect the weaker members of the crew due to his kind, protective nature. He is often seen protecting the Straw Hats even when he's out of his depth.
Sanji was never meant to fight Kizaru this arc. It's not his purpose in the story, just like when he didn't fight on the rooftop. Instead, we saw him saving Momonosuke and Chopper, highlighting his quick thinking and protective nature that we see throughout the story.