Zoro still beat a first Yonko commander, he hasnt done too bad. Kaido was always Luffys opponent so ZKK wasnt gonna happen.
It's not about the fighting here, Zoro got powerups and feats, he is strong.
That's not the problem.
The problem is that Oda setup and baited moments about Zoro leading the samurai of Wano, Zoro discovering his lineage conecting him to the Shimotsuki and Ushimaru + Ryuma.
He had a revenge plot against Orochi for Yasuie.
Then Oda just dropped all of it, and made Zoro fight King, who had 0 conections with him. It felt like a weightless fight, it was just spectacle.