The Army's current thought process (such as it is) is fundamentally flawed.
In the event of an emergency, you need to rely on standing forces, not wait for a call up and muster. Conversely, when participating in deployed operations, beyond Roto 0 there is ample time to mobilize.
Thus, simple logic would suggest that the Reg F needs to have the Domestic response task, and the Roto 0 deployment task; for subsequent rotations the Reserves should be heavily leveraged. Which suggests that you put the high training cost skillsets more heavily in the Regular Force as those have much longer timelines to generate.
Of course, that suggests that the Army would take a holistic approach in assessing its requirements, and balancing forces between part and full time; instead, there seems to be perpetual competition within the Reg F between corps and regiments, looking for internal dominance and advantage regardless of the cost. So we penny packet out fleets not based on a plan but on the desire of this, that or the other regiment to have the same toys as the others (thankfully, the worst example of that thought was stopped before it was purchased). We reverse engineer plans to reflect the need to maintain the infantry balance of terror - and so the answer to the number of battalions needed must always be an even multiple of three.
Meanwhile, we were taking upwards of a year to prepare forces for deployment; if it takes a year to train the Regular Army for deployment then they're taking money under false pretences.
In short, if we want to look for dysfunctional messes that waste resources, the Reserves, sadly, do not hold a monopoly.