since we know it is very unlikely that Luffy would let others fight Kaido so.... how about this scenario
Luffy is in middle of fighting on par with Kaido but then Suddenly BigMom after defeating her opponents joins the fight and it'll become a 2v1 on Luffy
Luffy somehow managas to keep up with both and defeats BigMom but at that Moment Kaido once again doing his cheap shot like he did with Oden but this time Luffy is critically injured/pierced and falls to ground
it is that moment that Zoro who has just finished fighting King comes in and see how Kaido hit Luffy
Zoro thinking Kaido Killed Luffy become Enraged and so furious that he goes complete Asura Mode and jumps toward Kaido screaming
They clash and Kaido is Pushed back and after few exchanges comes the final scene where Zoro cuts and Kills Kaido with a Gigantic Asura's Slash
and That's how he kills the eastern Dragon, Becomes Saviour of Wano, and fulfills the legacy of Ryuma once more....and for him Hitetsu forges the greatest sword he has ever made Ranked among 12 Saijo O Wazomono... which Zoro will Blacken it along with Enma and Wado IchiMonji whom he had already blackened during fight against Kaido ( Enma becomes 12 Supreme too, not sure about Wado )
....How is that for story making for Zoro to shine hehe