I never said Kyoshiro is his last fight.
I think Kyoshiro is Zoro's SOLO MAIN fight. But after he's done with him. Zoro will have enough stamina to TAG TEAM with someone else against a calamity (King)
But Zoro always deals with his shit alone. He dealt with Kuma alone too. Zoro being outmatched in strength against an opponent doesn't necessitate him having to tag team with anyone. Oda always finds a way for Zoro to come out as the guy who dealt with the other guys alone.
Like Pica outmatched Zoro in movement speed and Zoro had ro use other people's abilities to deal with him. And so you see Oda made sure it's Zoro alone making a plan alone and using other people's abilities to overcome the distance and then deal with Pica alone.
Theres even things like Zoro vs fujitora the first time where he deals with it ALONE despite not winning and the second time they clash, Zoro doesnt help Luffy fight fujitora even if he could. No he waits for Luffy to duck out of the fight AND THEN starts fighting fujitora again ALONE.
And you know why of course Oda makes it that way. Because Zoro's dream is literally tied to him winning a fight alone when versus Mihawk.
Your idea of a tag team is highly irregular and is gravely unsupported by how Zoro is written and whaf Zoro's character is.
To be honest it's more likely Zoro just plain doesn't even fight king at all if this is supposedly the only other option. And if doesn't fight king you would have to explain why he's training before ever going all out and why hes foreshadowed to cut fire and all that.