It makes perfect sense though. Everything we know about Yonko's and Top Tiers in general, this showing against the Scabbards goes against all of it. Here is Kaido, flying around in his dragon form, painting himself a massive target, and barely doing anything to avoid or stop any of the attacks, when we know he's more than capable of doing so if he just enters back into human form. And now, after the combined strength of all the scabbards have failed to give him what he wants, he takes one of them out with absolute ease.