Wano was Zoro's arc
Every single arc other than Wano, he was nothing more than background character.
If you were one of those who thought he will defeat Kaido then you were being just delusional
its funny how people dont think wano was zoro's arc when
- zoro had one of the most important intro scenes to establish wano's setting, with an AMAZING double page spread where he murders a corrupt magistrate trying to throw him in jail on false pretenses.
- zoro was the one who had the closest connection with the arc princess, saved her, slept with her, inherited a sword from her etc.
- zoro was the closest to yasuie and the one with the most personal connection to the people of wano in general. luffy was connected by food with a random kid, zoro was connected by friends, family, and a lover. He was Yasuie's friend, he fought with and allied with his uncle's dog, the princess fell in love with him. His desire to fight for Wano was as personal as its ever been for him.
- he got conquerors haki this arc
- he fought the main villain in a tag team with luffy as well as having his own villain fight tied to the endgame lore of the setting
- he had an entire plotline about being connected to ryuma even more explicitly than just using his sword, with Ryuma being gassed up as a Joyboy-level hero of the past.
- he had a key flashback that went into detail about the nature of cursed swords, swords having their own will to be inherited and carried out by the user
- there was a scene that called back to one of his very first promises in Arlong Park, where until he fights Mihawk again "not even a grim reaper/shinigami will take my life"
and legitimately more. it was as much of a zoro arc as WCI was a sanji arc, zoro just has a different character and plot than sanji so the arc did not involve rescuing zoro from himself or zoro's emotional backstory with his abusive family, it dealt with different things like honor and reputation, duty vs desire, found family etc