Zoro or sanji will be major key player vs Doffy, kata, Kaido, Teach, Imu, ...
even against Pre ts villains, they did nothing to Crocodile, Enel, Lucci, Moriah
Luffy has had outsiders as help vs Main antagonist .
Zodo might clash kaido when luffy and co aren't fighting him but that's already enough
He isn't the reason why luffy will win