Debuff manpower modifiers (UK had manpower issues, and could not form an independent offensive of their own once d-Day was done. Soviet Union was also scraping their barrels after Bagration).
Perhaps make it so that after hitting scraping the barrel, you can only train "militia" or "light" battalions, i.e Volksgrenadiers. To better represent what happens when you do that, discourage even more to go for that decision and spam troops.
Reworked supply system. Make supply lines drain manpower. Perhaps also differentiate between horse supply lines and motorized ones. Maybe also attrition far away from your supply lines will cause manpower loss. Even more so if you lack trucks.
These might at least debuff manpower and make it less appealing to pump out many divisions and much equipment.
Perhaps make it so that after hitting scraping the barrel, you can only train "militia" or "light" battalions, i.e Volksgrenadiers. To better represent what happens when you do that, discourage even more to go for that decision and spam troops.
Reworked supply system. Make supply lines drain manpower. Perhaps also differentiate between horse supply lines and motorized ones. Maybe also attrition far away from your supply lines will cause manpower loss. Even more so if you lack trucks.
These might at least debuff manpower and make it less appealing to pump out many divisions and much equipment.