What do you mean by his stamina isn't looking great? Zoro's been fighting at a level much higher than he's required to fight against Katakuri. I agree Zoro isn't tagging Kuri easily but he isn't exactly a sloth. King is super fast much like Marco. Zoro never had issues reacting to King or his attacks. He's going to do just fine deflecting Katakuri's attacks. Obviously, he isn't avoiding all of em but he won't be nearly as helpless as Luffy. He also has better endurance than Luffy.
Katakuri attacks at a much higher frequency, from every possible angle while King sits in the sky a lot giving Zoro time to breath.
Zoro is not slow but Katakuri is faster than both Marco and King. He danced around Snakeman while being severely injured, that feat can't be denied.
I'm not saying Zoro is getting stomped. Someone like Katakuri that specializes in dogding and counter fighting is more difficult of a fight for Zoro because his brute strength and lethality has a much higher chance going to waste when it doesn't connect.