That's actually interesting! So Kaido could have encounters with Dragon in the past. Did Dragon defeat Kaido as well?
I mean, we know Kaido was imprisoned before, several times. But these things need to be happen before he arrived in Wano.
Also a huge theory of mine, from years ago, was that Dragon originaly was part of the marines, like his dad Garp. So he was raised as hero from the marines, fell in love with a
Tenryūbito , which got pregnant by him. The world government and Imu couldnt let that happen (a child between a member of the D.-Clan and a Tenryubito), so Dragon and the woman need to run away. She managed to give birth to the child before anyone knew she was pregnant at all. But then they got caught, she was drown deeply into maryjoa, without any way to escape, maybe even caged down and this is way Dragon left the marines and changed to the revolutionaires. For once, to free his loved woman, for second, to give his child the possibility to life free.
But whatever, what i was going to was, if he was part of the marines, a trainee by his dad (Garp), it is possible it was Dragon himself which imprisoned Kaido the years several times. So the king of beast could be taken down only by an even greater beast. And when the marines lost Dragon, they lost the possibility to cage Kaido.