Did you notice how debates and essays about army structures in the past years have centred around some patterns for deployment into interventions? It's either x brigades* deployed, y brigades recovering representing some deployment (occupation) cycle or the focus is on rapid intervention with the brigade being tailored towards air lift suitability.
Other motives are powerful in the background, as saving officer slots and HQs from cuts, but they are always there when budgets aren't unrestricted. The historical anomaly is as far as I can tell the focus on interventions - and this didn't go away after the 2014 Crimea crisis at all.
A quick reaction force for Eastern Europe to be garrisoned in Germany, Benelux, France or Italy ought to be very road-mobile, not air-mobile. Air-mobile forces make sense only for the U.S. because of its crazy large (and expensive) military airlift capacity. They could actually deploy a couple weak brigades before heavy ones would arrive by ship. Other countries could air-lift so little, they would need that capacity to deploy (or refuel) their air forces. And their air forces have no incentive to prefer army needs over their own ones.
Here's another way to look at army structures: Plan for the big thing, not for the quick and short thing. Expectations for a quick end of a military conflict have proved illusory all-too often already. Only fools and people ignorant of military history expect to prevail in a military conflict within weeks or months. There are such exceptions and anecdotes of successful coup de mains, but it would be irresponsible to deter with a focus on this kind of scenario only.
What's needed for a big (100 brigades or more) and long (~2 years) military conflict?
Mass. And almost all of this mass has to be ready within months - neither weeks and nor years; months.You need a fine force early on, to avoid being defeated by a strategic surprise coup de main and then you need to move your mass into the scenario, preferably quicker than the opposition.
You would need the capability to mobilize. Now what do you mobilize? Reserves. You cannot train reserve brigades from a bunch of civilians to a brigade read to go within months.
Where do reserves come from? Training on active duty. What else other than reserve formations requires reserves personnel? Replacement for attrition, to be integrated into deployed forces while they're held in reserve for a few days or weeks.
A common feature of army structure debates and essays is the assumption that authors toying with fictional Orders of Battle may disregard the issue of reserve manpower pool generation.
This is dangerous in my opinion. The military bureaucracy serves its own ends in such debates, and this has to be corrected by political and public oversight as much as possible. A systemic neglect of an important aspect such as the deterrence of a long (more than two months) conventional conflict by those outsiders does warp the outcome into something even uglier than what the bureaucracy wishes for its own good.
2009-04 Modern-time Landwehr for Germany
2012-12 TO&E debates
*: All talk about brigades here is because "brigades" requires no further elaboration. Personally, I would look at lower levels much more..