[Yoda]

The nuances of superior ball striking reside in the left wrist. Or does someone think that perhaps plane, or a driven sweetspot is hardest to come by?

This is a great sentence, Okie. And the fact you could phrase the Three Imperatives in this way is a measure of your progress. Congratulations!

To your question . . .

The three are inextricably intertwined. Improve one, and you improve the others. Conversely, lose one, and you lose the others in a proportionate amount.

Regarding their heirarchy in the Application (and Control) of Force (2-L), you correctly have identified the Flat Left Wrist. It is no less than The Gateway (4-D-1) because it Harnesses (2-L #1) Centrifugal Force (Clubhead Control / the Law of the Flail / 2-K-#1, #2 and #3) and enables a precision control of the Clubface (2-G).

Adherence to the Inclined Plane (2-F / Clubshaft Control) makes the Flat Left Wrist possible because it eliminates (2-L-#2 / Avoid) the necessity to throw the Clubhead toward the Ball from its Off Plane location (Compensating Force Vector / Overpowering per 2-L #2).

All of which enables the player to maintain the stress in the Shaft (Clubhead Lag Pressure / The Secret / 6-C-2-0/A).