He was a fairy tale villain, not a modern villain.

A fairy tale villain is evil by virtue, bowser is always bad and will always be bad.

Modern villains are more about becoming evil under the right circumstance, and serve as a warning of why you shouldn’t let that circumstance happen.

The ending was all about that there is always evil in the world, it just needs to be contained by the hero.

In a modern story, it’s more about society overcoming systematic struggles.