On the bolded bit, Sanji
This was in his first Vivre card. According to Oda Sanji performs a role akin to that of a Staff Officer for the the SHs.
Right Page 2nd image on the extreme left.
With his quick wittedness, he occasionally saves the crew from perilous situations.
Sanji is an existence akin to that of a Staff Officer/Advisor
Nothing is 100% till we see Sanji matched up against him. It's pretty obvious to me however.
Hell in this chapter alone, you can pretty much tell who won't be Sanji's opponent given how they were treated against Aokiji.
Portrayal is key.
With regards to the the King argument, it was obvious Sanji wasn't going to fight him reason being that he's Kaido's strongest commander any one that thought otherwise isn't reading the story properly. Only way Sanji could've fought King is if Zoro was given someone stronger. Pending that Queen was always Sanji's opponent. With regards to Nami, I'm not saying she can't fight opponents much stronger than her. I do however think that Staff Officer rank is too much for her. To me it's the equivalent of pushing for Nami v a Calamity on Wano.