Not another fucking flashback, a summary. Uhhh a character arc is a transformation or development and bud, going from a selfish prick to a selfless prick is still a character development
Oh so you do want to get into it. Let's
Let me modify you definition there. Let me add the word "gradual"
It's called an "arc" because it's a gradual process right?
And said process is moved along by conflict.
An easy source of conflict for a character arc is "needs vs wants". An example I always like is, "Zoro wants to beat Mihawk vs Zoro needs to back off and travel the world to get good first". This creates BOTH external and internal conflict for Zoro. Externally he almost dies to Mihawk and loses his swords. Internally his frustration gets to him about how weak he is. Ultimately there's a change, Zoro pledges to luffy that he'll stick with him around the world to make him pirate king and never lose again god his sake. And of course we see much later that Zoro grew from this. He meets mihawk again and DOES NOT even claim that hes ready for another fight. He still has a journey with luffy left before he can hope to win.
Now to oden. Oden WANTS to leave wano and guess what, Oden NEEDS to leave wano as well. Already there's a problem here. His wants are the same as his needs. Oden wants to leave wano for unspecified reasons of being a guy who just wants freedom and then Oden needs to leave wano because the plot of the prophecy and finding one piece exists outside of Wano.
Therefore there is no conflict. Get it? Oden wants exactly what is needed by the plot.
You say Oden changed but where is the process of change on screen? What prompted the change? Remember oden wasn't an uncaring brute BEFORE he left. He literally took over and cleaned up kuri. Then when he returns his mind set hasn't changed. He finds out orochi is being a scumbag and just like with how he charged to beat up Ashura doji. He charges to beat up orochi. He even says the same thing. He decided to take over kuri because it was a wasteland and again he decides to take over wano from orochi because orochi is making it a wasteland. He actually says stuff like "I didn't want to rule but I would still be better for this country than you (orochi)."
So once again, he seems extremely the same.
You can say maybe the change happened between the mountain god business and taking over kuri but again WHAT ACTUALLY HAPPENED to cause a change? There was no conflict on between. Oden didn't care about getting banished so that didn't change him. We don't see anything about his jour eys around wano being what changed him. So what is the conflict?
You can probably say stuff like Oden wouldnt dance day and night for the citizens at the start of the flashback but even that's unconfirmed. For one, Oden showed he was Fine getting bad reputations for some random guy like kin'emon so him getting a bad reputation with the dancing shit isn't a change.
In fact we can't even tell how Oden has changed in the face of actual physical adversity. Like Oden couldnt reach Orochi through the barrier and he couldnt just molly wop kaido. This is the first time hes actually outmatched physically. But does that matter? No. Because this is the first and last time. Theres no example from before where we can see how Oden USED to deal with being outmatched physically and then we compare to it to how he deals with being outmatched physically NOW. So again WHAT HAS CHANGED?
I'll give you one thing. The clearest actual change in Oden’s character is this. At the start of the flashback he's not a man of faith. He cuts down the "sacred" mountain god claiming he doesn't give a shit about god's or superstition. At the end of the series Oden is a firm believer in the prophecy of Joyboy. That is the only change ice actually seen in Oden’s character. He became a man of faith. BUT ITS STILL BAD. Because the way he became a man of faith is a mystery because it's the one piece that made him like this and we can't actually see the arc that changed him to be this way.
The only tangible character arc he has is off screen because plot and so this flashback remains the same steaming pile of shit it was designed as.