1. Whitebeard’s strength compared to Kaido
In One Piece, Whitebeard was dubbed the “The strongest man in the world” at that time. Of course this is not a nickname just for fun, Whitebeard’s wanted level is even second to Pirate King Roger.
In the era of 20 years ago, Whitebeard was still stronger than Kaido, because at that time Whitebeard was still in the peak of his peak. Once a member of Whitebeard’s crew, Oden probably knew just how strong Dad’s power was. So why does Oden say that no one can beat Kaido? What exactly caused Oden to believe that nothing could push Kaido out of Wano?
2. No one has the opportunity to ask for help from outside?
The only person in Wano who could win against Kaido was probably just Oden, but Oden was on the verge of death, so it seemed he wasn’t sure he could fight Kaido at the time. Of course, this means that all members of the Nine Red Bao are also at risk of being killed by Kaido if they try to fight Kaido and Orochi.
If that happens and Kozuki Toki doesn’t send them to the future, then no one can contact Whitebeard or someone out there, because no one is strong enough to get out of Wano. In other words, Wano will remain isolated, without anyone knowing that Wano was invaded by Orochi and Kaido.
3. Izo knows nothing about what happens in his homeland
There are two possibilities for why Izo did not come to rescue Wano with Whitebeard. First, Izo and Whitebeard don’t know what happened to Wano. Eventually, by the time they found out, it was too late and the news spread was the death of Oden and his allies.
Whitebeard is not the type of person who wants revenge, so he will not go to Wano to avenge Kaido’s actions, when he hears that no Kozuki clan survives. It was hard for Whitebeard to attack Kaido if the war harmed both sides on a large scale.
The second possibility, Izo knew Oden’s plan from someone (possibly Denjiro or another unknown character) and was waiting until 20 years later to act. If this second possibility occurs, then we can expect Izo to come to Wano to help the Nine Commentaries.
4. Oden wants to make sure that the Kozuki clan will accompany Joy Boy’s successor
Because Oden believed there would be a big fight in the next 20 years, or rather in Luffy’s time, Oden of course hoped that Joy Boy’s successor would be accompanied by the members of the Kozuki clan.
Therefore, perhaps the reason Oden asked Toki to send Momonosuke and the others until 20 years later, was not only because no one could depose Kaido, but also to make sure Momonosuke was still alive. Sound Oden believes he will die and when they resist, there is a danger of Momonosuke being killed.
If Momonosuke is the main heir of the Kozuki clan killed, of course the Kozuki family will have their blood vessels cut off and no Kozuki successor will be able to accompany Joy Boy in the future.