Couple thoughts on this;
First, we are a product to a degree of our British heritage; ie aristocratic officer corps focused on leadership not technical training.
Second, we prioritize combat units and formations. Those are the Comd billets that get you promoted and they overwhelming go to cbt arms rightly so, however there are very very few CS or CSS units and formations for non cbt arms types to get the needed Comd time to be seen as GOFO or CWO potential.
Third, Comd is tied to promotion and promotion is tied to Comd. It’s highly highly improbable that our personnel would get promoted to a higher rank or position from a staff stream. Ie a general staff model where you might go from Maj to Col as a sustainment planner progressing through tactical to strategic planning developing a highly proficient technical knowledge. This circles back to point 1 where we value “leadership” over technical expertise.
Fourth, the size of the overall military, its various trades etc. leads to a belief I think that we can’t afford to be specialized as it will limit employment and flexibility in the force. The size of the military I think has also led to most GOFOs and CWOs focusing only on their institutional leadership function as the military is not large enough for them to get much time or experience as actual force employment commanders conducting war fighting. That institutional vs war fighting dynamic likely has significant impacts on the direct operational war fighting mindset of our senior leadership.
For the army it will be interesting to see where the new CS and CSS brigades go in terms of personnel and how that affects the army. Ie the Army routinely believes that the lead planner should be cbt arms in a formation. That’s true of a manoeuvre Bde but does it hold true for the sustainment Bde or protection Bde? Likely not.