Not surprising, considering the same person was claimed in his prime to be Kaido's rival.
I'm now wondering whether the claim was factually correct or just another Morgan-ism. If the former, Kaido must have broken his will (ie what haki is based off of) to so much extent that the upstart SH crew of 2 years was ago was able to handle him just fine. And if so, it's quite possible he got the Shichibukai deal prior to losing his crew, which makes Jimbei OHKO-ing him and Doffy telling him that he no longer belongs to the warlords' league much more meaningful.