The whole "cybernetics" field is pretty weird to me, I think the notation and lingo have sort of moved on (I could easily be wrong and biased without realizing)

The whole "cybernetics" field is pretty weird to me, I think the notation and lingo have sort of moved on (I could easily be wrong and biased without realizing). However the theorems you are talking about have useful, well studied analogs in the field of control theory. For example the Law of Requisite Variety is very much related to the concept of under-actuation (https://en.wikipedia.org/wiki/Underactuation https://en.wikipedia.org/wiki/Underactuation). The good regulator theorem becomes the internal model principle. https://en.wikipedia.org/wiki/Internal_model_(motor_control) https://en.wikipedia.org/wiki/Internal_model_(motor_control) I think you'll have much better luck finding good introductions to these topics in control theory than in trying to learn more about cybernetics.