The state that remains is often simple enough that plain old React state management with useState/useReducer is sufficient

hah this is an understatement. For hooks, the React runtime already does a ton of non-standard-js things under the hood. useState gives a method to update and "subscribes" a component to updates on the hook's value. Put that code in a custom hook, export it and you re-invented Redux. In fact, exporting a single big useReducer for all your state gives you something almost identical to old style Redux.