Zoro fights Kaido and BM in Wano
what did your boy Sanji do in his own arc? WCI? Hmmmmmmmmmm
History might repeat itself for Sanji in Onigashima... be prepared
Zoro is fighting BM and Kaido in a group battle with mobility assists.
BM and Kaido are tanks who prefer to engage with their physical dominance rather than act as mobile speedsters outmaneuvering their opponents.
It's intellectually dishonest to say Zoro has "fought" Big Mom in any real sense, might as well say the other Strawhats who trolled her earlier have that feat too.
Fighting 4vs1 to temporarily BFR her when she is serious is a decent feat, but it's not proper fighting, I have no doubt that Sanji could have replicated that feat if assisted by 3 others. (Kid and Law who did the most direct work).
Zoro hasn't really "fought" Kaido either, it's all been sneak attacks or blocking them trying to sneak attack Luffy, very few times has Kaido
targeted Zoro directly. But I'll say this claim is fairer than the BM claim. Though when he fought aerial Kaido he needed a mobility assist which he wouldn't have against King, and Hybrid King is more agile than full the Zoan Kaido who outmaneuvered Zoro.