What I would like to see in this subject (and in general, in all game aspects) is a flexible system, which permits you to micromanage or not.
Basic models for each division type, based on original national doctrines, and subjected to tech research or experience/army doctrine advances should be available. But you should be able to configure your division toe/oob to an extend and the produce that type of division all the times you want.
Basic unit should be division (with the ability to configure vrious types, or modify some of them individually, like elite units). The point of having elite units in real-life was giving them better training, best equipment and higher number, so they would be able to overcome special difficult tasks, but they consumed more suplies and their fielding was higher in time & cost terms and training. So the avility to make an army full of eleite divisions should be available to the player, but wouldn't be practical in relity.
As I said basic unit should be division, with corps being the following one (from 1 to 6 divisions), armies & army groups would be represented by HQ units. Option to allot divisions & corps to armies, and armies to army groups should be available. Corps & armies should be able to be equiped with extra regiments/bdes. Armies & AG should be an specific range, modified by tech, doctrines & maybe leader skills/experience. Units experience must be introduced and have an important factor in combat outcoming.
To tke full advantage of this model, province divided map model must eb abandoned, to return to an other type of equally distributed space model (be it hexes or whatever). This space units must have a range of staking limitationsfrom 0 to X, no penalties, from X to Y penalties cused by logitical issues and cogestion, being Y the maxim number of units per spce unit. This will give us a realistic fighting feeling and outcome; making strategical maneouver and encirclement, breakthrought and other modern war doctrines more important than ever. But that's n other question.
I'm in favour of dropping MP points for realistic numebr management and making countries differences in OOBs possible. i would say even more, I think it would be neccessry for what i exposed above.