Sanji turned the flying fish riders on his side and they call him ''young master'' and respond to his call.
Sanji turned the marines on his side and was leading them. Not sure how the word ''fodder'' makes it lose weight? All armies are made out of fodder. The Samurai Zoro wanted to round up are also fodder.
Sanji turned viola on his side.
Sanji was in charge of the SH Crew after DR.
Sanji turned pudding on his side.
Sanji turns enemies into friends and we had actualy moments of him leading people. So yes, Sanji is much more a leader than Zoro - cuz Sanji actualy did it multiple times. But you ofc will say he is not, cuz ''reasons''...it's like saying Zoro can fly better than Sanji, while never been able to do it.
It can't happen, the war already started...Luffy rounded them all up. Luffy got Hyogoro on his side, he showed his charisma and showed the samurai in Udon that he is serious about taking down Kaidou and won them on his side. And because Luffy got the boss to his side, the rest of all the Samurai from Wano also joined.
The Samurai were split up in different groups with different leaders. Zoro is none of them. Why would Zoro all of a sudden be the leader of them?