That's what he did
Zoro already cut dragons to parallel ryuma : at PH and against King
Oda gave zoro a fight against King as a way to say you're surpassing low budget Kaido while Luffy gets to save Wano from a dragon zoan pirate who's WSC.
The thing is:
I'm not against the author giving opportunity for other characters to take the spotlight and defeat the main villain of an arc. I was an advocate for that during Dressrosa and WCI, but Oda simply didn't go for that route. It's always "the luffy show". So I kinda don't expect such a detour in Wano.
But I also hate repetitive sequences, especially in the same arc. Making Zoro cut a fire dragon from King just to have Zoro cutting ANOTHER fire dragon in Kaido later? Eeehh....I just wouldn't make King use a Fire Dragon out of nowhere instead, and save the "dragon cutting" for Kaido if it was the plan.
But hey, it's Oda. I think his writing of Wano, and Onigashima in particular, is a complete mess. So, who knows.