@Koyomiya
There's also the fact that Oni are routinely hunted down. Only the most powerful and viscious survive, leading to those traits being passed on. Either through genetics or nurture. So in a way, Momotarou actually amplify the berserk nature of Oni.
If the Oni were left well alone, who's...
Why is the go-to always lack of communication? It's a serious problem in a real relationship, but in stories it's just a minor inconvenience to be brushed under the rug.
I mean sure, 'drama' can lead to 'progress'. But this kind of drama pretty much never does in my reading experience.