Last time there was a first mate and a chief of staff on the same crew they were equal in strength so shiryu can still be >= than Lafitte even if lafittes chief of staff.
and Sanji has beaten people higher in hierarchy than Zoros opponent before. Remember Thriller Bark Sanji fought the commander of the General Zombies and Zoro fought a general zombie.
Iam not talking about strength, I am talking about authority. No BB commander has been stated to be the first mate and only Lafitte is a chef of staff. Lafitte is above Shilew in authority. And Oda will never have Sanji fight someone above Zoro's opponent in authority in the final battle against their rival pirate crew
And using Mohji and Cabaji is a bad example because one of them was a first mate, and the other was defeated by Luffy, and it was in EB when it was just Luffy, Zoro, and Nami.
And in TB, Moria's commanders followed a theme that pit them against the weak trio members:
Perona->Ussop
Absalom->Nami
Hogback->Chopper
Zoro didn't fight a commander because Oda wanted to give him a solo fight for himself without any drama to replace Shusui and to introduce Wano lore. Saying Sanji fought someone above him that onetime which means he can fight Lafitte is like saying Chopper will fight someone above Shillew in the BB pirates. Neither will happen. Sanji will likely fight Pizaro