If you really think about it, King and Queen were stepping stones for Zoro and Sanji getting their powerups this arc, just like Ennies Lobby. Zoro was getting low diffed by King, then Enma awakens, then Zoro low diffs King, so mid diff overall.
Sanji was getting low diffed by Queen before his Germa awakening, then he breaks raid suit, then low diffs Queen, so overall mid diff.
Sanji was getting low diffed by Queen before his Germa awakening, then he breaks raid suit, then low diffs Queen, so overall mid diff.