Dragon Kaido would take more damage than Zoro receiving same attack from King.
Unlike Zoro who likes to parry attacks with his sword and he's damn good when doing that, Kaido is the the type to just eat the attack and endure it.
Dragon form which is an easy target will be slashed badly, just like when Oden and Zoro slashed him.
P.s.
Zoro had already come and witnessed the monsters in Rooftop. He has faced Dragon, Base, and Hybrid Kaido. He has faced all out Big Mom.
Yet the moment King gets more serious, Zoro still gets impressed and acknowledges him as "he is strong!!!".
He already saw the strongest monsters in Rooftop yet King still easily impresses him.
So much for OPlers who think "Zoro has faced 2 Yonkos in Rooftop, King will be a walk in the park".