We might have to start admitting that Sanji is second strongest. It seems Oda has changed the dynamics of the crew.
At Dressrosa we saw Sanji become acting captain when they left Luffy and co there. Then Luffy said he can't be PK without Sanji. Then Sanji received a higher bounty than Zoro. This I think was the final nail in the coffin as subconsciously Oda thinks Sanji is stronger than Zoro.
I think Zoro fears it too. This is why he pulled out Enma for base Sanji. He was insecure about how strong Sanji had become.
So Sanji vs King is to be expected. He is basically VC in all but name.