ORIGINAL: ncc1701e
People disband planes to buy land units: tanks or armies. Why? Because obviously, there is a lack of land units.
There is always a lack of ground units. Even if the Russians received the extra 5 Armies you state they should have they will still want more (at least I would). So Since air units, especially for the Russian, are not very effective, the smart players will still disband them to build more ground units. But this will hopefully all change with the next patch.
Retaking this list:
https://en.wikipedia.org/wiki/List_of_Soviet_armies
There are 12 Infantry armies that were formed in 1939. On the game map at the beginning of Europe 1939, we have only 2 Infantry armies. We need for Russia more armies. Bad ok, but more.
Germans must have the feeling of quantity. Three solutions:
1. put more Infantry armies on the map in Europe 1939 scenario
2. put more reserve Infantry armies in the Deployment queue in Europe 1939 scenario
3. a combination of both
Again, my preference would be to have higher quality (41 tech) Russian Units.

