Just like Katakuri was superior Luffy in almost every aspect
(Haki: better in CoA and CoO, especially CoO
DF: Katakuri used his DF for elasticity purpose too. Additionally, it provided stickiness. Moreover, he used his DF like a Logia (partially thanks to it being a special Paramecia) and his DF was awakened
Agility/Speed: Katakuri was as fast as Snakeman and could clash evenly against it.
Weapon Use: Unlike Luffy, Katakuri is a spear user and a master marksman.)
King seems like a superior Sanji in almost every aspect too.
(Haki: don’t know about his CoO but he could kind of react to invisible Sanji. Don’t need to talk about CoA I guess.
Agility/Speed: King, compared to Sanji, is more agile in air thanks to his DF and his wings. Moreover, he seems pretty fast too.
Durability/Endurance: His DF seems to provide better endurance than RS.
Strength: King seems to be more adept at kicking. Moreover, he is using a power extremely similar to DJ, which might be more powerful than Sanji’s fire.
Weapon: Unlike Sanji, King is a sword user.)
Katakuri fight was a turn around for Luffy as it symbolized him surpassing his superior version. King, to me, seems like superior Sanji and this is exactly why I believe Sanji should, with or without help, take part in King’s fight to symbolize Sanji surpassing his superior version.
In my opinion, superior Zoro might very well appear in one of the next arcs (Elbaf, Lodestar, Edd War? etc.) and that might be his turn around moment.
(Zoro is strictly a swordsman, his opponent might be a more adept swordsman with other fighting skills too. However, King, if anything, seems more similar to Sanji in terms of power)