Luffy Fought Evil Fish (Arlong) ---> Zoro Fought his Top Commander (Hatchan)
Luffy Fought Fake Hero Warlord (Crocodile) ---> Zoro Fought his Top Commander (Daz)
Luffy Fought Invincible Destroyer (Enel) ---> Zoro Fought his Top Commander (Ohm)
Luffy Fought Elite Squad's Top Member (Lucci) ---> Zoro Fought Elite Squad's 2nd Top Member (Kaku)
Luffy Fought Creator of Nightmare (Moria) ---> Zoro Fought his 2nd Top Creation (Zombie Ryuma)
Now let's check Post-TS:
Luffy Fought Evil Fish 2.0 (Hody) ---> Zoro Fought his Top Commander (Hyouzou)
Luffy Fought Fake Hero Warlord 2.0 (Doflamingo) ---> Zoro Fought his Top Commander (Pica)
Luffy Fought Invincible Destroyer 2.0 (Kaidou) ---> Zoro Fought his Top Commander (King)
Luffy is going to Fight Elite Squad's Top Member 2.0 (Whoever is Imu's Top Vessel among Holy Knights) ---> Zoro will Fight 2nd Strongest HK
Luffy is going to Fight Creator of Nightmare 2.0 (Whoever is Writing this OP Story) ---> Zoro will Fight his 2nd Top Creation (Mihawk)
It's this Simple,
If Zoro Fights anyone else, it's gonna fall under category of Fights similar to Lucci or Killer or Braham or T-Bone ... etc
Basically, Filler Fights, rather than Core Fights that are necessary to Win the entire War.