The rooftop battle is close to impossible to win for those guys. Big Mom barely did something. Kaido in base could have already speedblitzed everyone who's there, bar Luffy, into a coma.
Hybrid Kaido is already hardly beatable by himself and that's him not even showing what his awakening can do. Same with Big Mom and her different stages of power: She's gonna show her awakening abilities aswell, which are most likely far superior to the stuff we've already seen.
With a legend like Oden there we can see how he fares against that hybrid (+awakened) form and how Zoro and Luffy compare to him.
I didn't know I needed this, before it actually happened. Now I really want that stuff to happen.
Obviously Oden would be time limited or something like that. So he might just be there to stage for Luffy until he transitioned to the next level, granted that he was completely fresh when he presumably was back in the past for his execution.
All in all this might legit be a very cool move from Oda, IF you give it a chance.
