Kaido is still stronger than any admiral. Ryokugyu finishing off weakened commanders shoudn't change that. Base Kaido without ACoC ran over the Scabbards like a train. And Luffy should be ~ Kaido in a 1 on 1 and both being fresh.
It's Oda's way of saying that they are equivalent in power and that Luffy didn't surpass Kaido alone, probably Oda considers every help Luffy had to be equivalent to Kid or Law's contribution in defeating Big Mom, 50%.