Again, the manga explains characters cannot increase the strength of their CoC by training their CoC. It can only grow stronger by the user growing stronger.
Characters can only train CoC to become better at controlling it.
That means you cannot determine the strength of a character's CoC by how strong they are with their CoC. You have to look at their strength without CoC. The stronger a character is, excluding CoC haki, the stronger their CoC haki is.
The SBS doesn't debunk anything I said. Nor does it go against the manga. Rayleigh saying people usually have natural affinity for a specific type of haki and Oda confirming it in SBS just means character usually have a haki they will have an easier time learning than the others. It has nothing to do with the strength of their haki. That just hard work versus natural talent and hard work to beat out natural power.
WE don't know everything Shanks can excluding ACoC. So to say ACoCless Shanks can never beat ACoCless Kaido is just an assumption. Compared ACoCless Kaido to rooftop Zoro. Do you think ACoCless Kaido is much stronger than Zoro? And if he is how much?
Zoro's offensive power, defensive power and fighting skills pushes ACoCless Kaido to extreme diff at bare minimum. There's a great argument to make Zoro can win.
Plus Shanks is better at using ACoC than Kaido. The manga states characters can't train to control their ACoC. Even if Kaido's ACoC is stronger than Shanks' ACoC, Shanks' ACoC skills and easily makes up the difference