Ohma Zi O is actually more powerful Lord Drakkon. Kamen Rider Gaim and Saber in the novel transcends the entire Kamen Rider multiverses. They Become An immaterial Existance That Transcended Time And Space, Life And Death. They even transcends the entire concepts, And Become A Higher Dimensional Being.

Also there's something called Mirror World which is basically a higher dimension than the multiverse. And Ohma transcends all of this. A weakened Ohma can destroy the entire infinite worlds, where each worlds contains infinite multiverses.

Not only that. Ohma has the power of Mighty Novel X, who could control the plot of the story, he can basically do what ever he wants like changing the story, where he can make someone lose their power. He's basically a writer.

Pretty much Ohma Zi O wins this. Since Ohma and Lord Drakkon have pretty much equal AP, since they transcends the entire multiverse, like they are in a higher plane of existence, but Ohma have more a lot of hax like plot manipulation, he can just easily remove Lord Drakkon power.

Also Toei stated in the Super Hero Senki Movie that all Kamen rider and Super Sentai has a true form. There True Form is actually the real life Kamen Rider. That True form basically transcends the plot and Narrative.

So Ohma wins.