It was always obvious Kaido had an hybrid form. Kaku could go hybrid shortly after consuming the fruit. And Kaido had the fruit for around 18years to the confrontation with Oden, so more than enough time to have hybrid.
The implication of the Kaido vs Oden battle then was never about straight feat battle estimation, but portrayal, which was the hybrid wielding Kaido refusing a direct confrontation with Oden, coming fully prepared and out numbering Oden's group while having a spy in his group and still admitting he should have died that moment, with the recent chapters still putting Oden as one of the people who could fight / beat him.
Not only that but also Oda want to skip the battle fast. Who says Oden was already in all out version? Both Kaido and Oden didn't fight allout for sake for wano and the plot. A all out battle between these top tiers would effect not only udon but whole wano. The result would be that the country would end in a disaster, many people would get killed and cities would get destroyed. We see what happen if Top tiers fight each other(Punk hazard and Marineford) and wano would end in a disaster if these two would fight in a all out battle.
Oden is a top tier called with Rox,Whitebeard,Shanks and Roger. You can be sure if Kaido had his Hybrid, Oden would something equal to that form.
People should reread all the last chapters. One single slash of Oden did more then Luffy+Supernova+Scabbards against Kaido. And we see the insane power of Enma,ofc Zoro AP is high so he single cut a huge ass horn(over mountain size) with not even his strongest attacks.
Oden was natural powerhouse like Linlin and Kaido, he was physical a monster and he could control Enma + a other strong sword perfectly.
So imagine Kaido hybrid and Oden fightning all out> Wano would end in a disaster.
Because that Oda use the old hag to end the fight very fast. Even Kaido know it and kill out the Old hag because he know the fight would still continue and he had until now very much respect against Oden.
You can be sure Oden looking very good featwise since one slash of him outperform the entire attack list of the Supernova and Scabbards.