So the XP is not per unit. Its more like money.
We currently keep track of money pretty well, how hard is it to count the total value of IPC units you lost this turn?
Thats how much XP/Tech you got just “earned”. Its definitely hard to balance, but i think their could be some benefit.
I never understood, how researching a technology would instantly upgrade your units for 0 cost. While doctrines is a change in tactical thinking, using units differently. You don’t actually have to build anything or upgrade anything, but the techniques in battle change and represent a learning experience.
In real life:
Germany focus on armored manuver warfare, to encircle their enemies.
France focused on static defenses.
US focused heavily on heavy bombers and daylight raids.
While Brittain focused on night bombers.
Russia focused on heavy preliminary artillery bombardment, for battles.
while the US had artillery available quickly to lower lever units. (“RADIO”)
Japan developed the expertise and techniques for night battles.
I think these things add a little bit to flavor in the game.