I don't think we North Americans run "all-in" armies anymore. Even y'all.
The new world order and the Ukraine experience have changed that. The new world order is limiting what we're prepared to do because of the cost; and Ukraine has taught us that attrition rates in Class A equipment is high. Both of those mean that manned reserve equipment is a necessity.
I'll certainly agree on the full-time side. Based on the overarching principle that "your army can only be as large as the country can afford and the government is prepared to commit," the place where you have to start creating savings is in the recuring annual costs. Full-time personnel not only eat up massive salaries and pensions, but also housing and support infrastructure, and recurring annual training costs.
I've been told by one CDS that protecting the human capital is the most important decision . I disagree with that. Keeping combat capabilities alive is important and that is through a judicious mix of people, equipment, and munitions. When the latter two fall below the critical point in order to save the first then your balance is out of whack.
I'm a firm believer in that and the ability to generate 3 x 1. In fact I see it as a double 3 x 1. A 30 RegF / 70 ARes structure is the first layer for a near combat ready units. Further, a proper 30/70 unit can be the mobilization base with the addition of 70% new recruits. In the aggregate, any battalion based on one RegF company and a share of headquarters and combat support should be able to generate not only a full battalion with its reservists but a light brigade in mobilization. In other words 10% RegF, 20% ARes and 70% new recruits. That's a good ROI.
If you support your industry properly and build it right then you can do better.
I question the term "anymore." I don't think that you ever could. WW2 started out with very few forces with any major level of mechanization. Even the German blitzkrieg armies were mostly horse drawn.
The only reason that there was an opportunity to build up the forces was the ability to convert existing industries far from the front lines to produce the implements of war in the gap between 1939/40 to 1944. After that was reduced to the issue of how to get that equipment and people from the factory/base to the front line.
This is why I'm more of a manned equipment guy. You need to be able to replace or replenish the division that you commit while mobilization (in the broad sense happens. Like all wars before us (except the Confederate army) a large part of your force needs to stay out of action to generate/regenerate the committed force. The only thing that I can think of that skews that is if non-repairable/recoverable equipment losses start to outpace personnel losses. I agree that that needs to be factored into the reserve stocks. That generally hasn't happened during conflicts over the last few decades (including the big wars which have all been relatively short). Ukraine is changing that equation, but then it is also changing the equation on heavy metal v munitions loss/ usage rates.