Maybe i'm wrong, but it sounds that you are re-inventing the ValueChangeNotifier class (Observer pattern).

After having read your article and watched the youtube video you've linked, you may have reinvented the ValueChangeNotifier mixin (Observer pattern)...

I think you missunderstood what is the needs of state management libraries. Don't forget that these kind of libraries are used to promote a global way to develop features for teamS (or a big team), where consistancy and maintainability are more important than complexity-free code. That's why testability is important, as a code 100% testable is a quality criteria, not complexity criteria...
At the opposite, if you are in a small team, then as said by Matt or Philip is the youtube video, take whatever you want, as long you are confortable with it. As long as "you're not fighting against the framework", as said by Philip !