Rooftop 5 had legitimate reasons to face Kaido as the leading Worst Gen members.

Sanji as a top Commander of the Straw Hats has his moments against Commanders of the Beast Pirates, the main enemy organisation in Wano.

Nothing strange. Yeah, Sanji might've been invisible when Kaido was present but there's no need for such to be honest, Sanji had his place and purpose in Wano, clashing with King to save Momo and defeating Queen both to protect others and for himself.