The whole point of Oden’s flashback concerning Wano was to show that Wano was a rich country with a lot of strong individuals but that Orochi and Kaido’s rule destroyed the country and the samurai’s spirit. This is why there is no more strong samurai except for Oden’s vassals who was the last Shogun (in spirit at least) of Wano.
Therefore narratively speaking they cannot have any strong samurais in the enemy camp. Furthermore, in chapter 986 Oda emphasis (by Hyogoro) that the samurai’s spirit was lost by having the Oniwabanshu and the Mimawarigumi changing side after Orochi’s death.
Zoro fighting a strong samurai will be anti-climatic. Which is why Zoro will fight a strong pirate swordsman instead.