And of course Oden tried to kill Orochi and Kaido first, but his first attack was unsuccessful (when he had just returned), so he just did the best he could do in the moment, not being a total maniac either who might have run himself out fighting all alone that moment, and he is someone who can talk and listen besides.
I guess he was counting on the representative value of the true leader or figurehead of Wano dancing like a fool, repeatedly in exchange for the lives of his people, being basically enough to appease Orochi's revenge. He might have expected those hundred(s) of people he saved (did he or didn't he? Apparently he did so far) were the extent of Orochi's revenge, rather than expecting him to want to literally kill all the country, until forever. And Kaido also had a word in this, as the true force and a pirate, and he might have expected to rely more on a pact with a pirate or that simply his scheduling is his priority.
The problem isn´t the day with you describt right, of course in that day when Orochi use the people als Hostage, Oden didn´t have really any choice and need the deal to save these people.
But the most user don´t speak about that event but more about the 5 years overall in whole, you guys didn´t can tell me that Oden didn´t even had the chance to build up a plan together with Hyo who he visited most time, that he didn´t have the chance to build up a plan together with the Daiymos. I mean his plan to kill Kaido wasn´t a bad plan, the current alliance try the same aswell.
He don´t even need Whitebeard/Roger pirates, alone with the power of himself and Hyo+Samurai it would be enough to take out Kaido and his crew. I know Oden didn´t want that people getting killed in this big war, but he didn´t have any other choice to take out Kaido either if he didn´t fight back.
In the end all Daiymos get killed, Hyo wife get killed and many other so much people, wano 20years later is a totally mess up. Oden should think about the consequences if Orochi would still rule over Wano, someone who want everyone in wano to suffer. I doubt that even Oden believe the shitty deal with Kaido and Orochi, someone who try to kill off Momosuke.
He had ways to prevent that, to stop Orochi and Kaido. That is the most point of many user here who criticism the decision of Oden
But I want try to understand the decision of Oden, I want to try to explain why Oden didn´t make a alliance with Hyo and co.
It is simple answer but I think it is overall about Oden pride, he was shown as the Men who handle everything alone, even if he let his retainer to come with him, he most like want to take out anything alone and be honest that is most like the point. He most like feel guilty for everything which happen in wano because he wasn´t their because of his adventure with Whitebeard. I think overall how Oda build up Oden character, that he want to save his country on his own as he feel guilty for all the bad things who happen in Wano because of him. More and more I read about the flashback, that is how Oda build up Oden character, his pride and badass decicion was something which was most fascinating about Oden character but also that is his most like his biggest weakeness in sametime. He didn´t want help from Whitebeard or Roger pirates, he didn´t want Hyo to suffer for all the things who happen because of him, he try to save the country on his own, different then Luffy who fighting together with Wano against Kaido.
Be honest I criticism Oden decision aswell, but if we really look how Oda build up him as character, I finally understand why he don´t make any b plan or try to make a big alliance with Hyo and co, overall because of his Pride. People can hate it or love it how he handle the whole situation, but I think Oda make a great job at least in this one if it comes to Oden character.
Was it dumb how Oden handle? Yes it was most like the worst decision with he take.
Was it lazy write of Oda overall? I don´t think, so if we really look close how Oda build up overall Oden character, we get in his flashback many hints that he was everytime the men who fight alone without the help of the others.
It is his tragic story and the reason why he lose his life in the end.
You see my previous posts that I didn´t like his decision either, but I re-read the flashback and I can at least now understand the point which route Oda choose here, also I don´t think he did this without a plan, since Zou arc the word about the foolish lord was already said, I think he plan this event since the Zou arc.
Overall I still enjoy the flashback and it still at least for me one of the best if not best.
Of course I still have some points which I don´t like about the flashback, as Oda didn´t focus on Toki more(but hey even in that point I think Oda gonna reveal more about Toki in later of the story of Wano, I think we will learn more about Toki later) and the legendary hour which I think he could take more time for this insane event overall. Also probably more focus on the retainers either, but overall it is still a great flashback for me, it was after all Oden´s flashback and his adventure at least his character get a great build up in my opinion.