Earlier quoted context omitted.
This is so sad but true. Redux-Toolkit now abstracts away the abstractions introduced by Redux & Co. in the first place. Think about that.
Not sure I agree with this statement. The Redux core by itself doesn't really introduce abstractions. A reducer is just a function. An action is just an object. They're not abstractions, just a particular usage pattern.
I do not agree with your argument; a reducer itself is an abstraction of state management, that implies quite a lot (pure function, immutable operations etc.) React itself (especially when considering the stable context API and hooks) does not introduce those concepts of reducers or immutable operations at all (except for the fully optional useReducer hook that was added, but not present in previous React versions). So its - at least to some extend - additional abstraction not present otherwise.