So basically Kaido had to take advantage of a huge internal crisis(Grandma/Grandpa/Orochi plot) which turned the country upside down
Then had to beg to sign a 5years contract keeping Oden away after he returned to avoid getting overwhelmed, dancing like a fool while Kaido was preparing things in the shadows
Even with all those preparations and with Oden's limited forces(only had the scabbard), he could permanently scar Kaido and almost kill him if not for the Grandma using Momonosuke's appearance as a distraction
No wonder Akainu, Kizaru, the World government think twice before trying to attack them