Since its a natural thing to get the best, dont think that is the most reasonable.
Maybe it would be good to limit the amount of unit at your disposal on the higher tiers so you are forced to have PzID, PzIIIH, PzIIIJ, every kind of artillery units, regular infantery and so on.
I understand that this is an extra difficulty but it would e more realistic, visualy more exciting and accurate historically.
It would also eliminate the incongruences of upgrading captured chars to PzIVF, for example. Captured Chars should remain captured chars till you consider them obsolete and you redirect its experienced crew to other unit.
Should indeed upgrading downgrade unit's experience?
Of course, I expect the poor russians also sending obsolete units to the fight.
