How are Kid and Law supposed to help? They don’t have penetration Haki like Luffy, and they have the same problem as Zoro - they haven’t beaten anyone notable.
And you do realize that in Yasu’s dying moments he literally said that nobody could take Kaido’s head while the manga showed Zoro...for some reason. That same Zoro went on to get Enma, which scarred Kaido.
And
@Zenos7 is right - you didn’t even try to address Oda’s purpose of Zoro getting the Kaido Maimer. Especially since Ame no Habakiri (which again, slayed the Yamata no Orochi in Japanese myth) is a well known sword in Japan.