Yeah but you also had Zombie Armies there, especially the Wehr, they could turn dead Volks and Pioneers into Grenadiers even without the Tier 2 building.
Certainly true, but Wehrmacht also had to buy their veterancy for a significant price for a limited amount of units at once as well back then, so arguably the theoretical issue "One side is a bit underpowered, let's add manpower upgrades for later in the game" would be still a relatively simple one if it were needed. If one faction had scaling issues with their infantry, an upgrade allowing them to make themselves have more manpower income later on could theoretically alleviate the problem as it would be expected said infantry will regularly lose fights and have to be reinforced more often, though this would enforce a bit of a micro tax since that means this faction would be expected to reinforce much more often than their opponents to stay in the game which is a whole other can of worms.
Annnndddd the ultimate Supply Yard upgrade also made Rifles vet faster in CoH1 for additional ammunition against my point since the upkeep reduction was definitely not the only thing fighting back against tougher tanks and Volksgrenadiers back from Hell.
...pls no zombie Grens
They are.
Grenadier have a Pop of 7 Pg of 9.
Conscripts have a pop of 6 Penal of 7.
A PzIV has a pop of 12.
A T-34/76 has a pop of 10.
There's a little bit difference there still though, since being delayed by 18 manpower per minute from getting 6 Grens instead of 6 Scripts is a less insurmountable deficiency than, uhhhhhh...only being able to have 3 Pak 88s while the other side has 4 HM-38s (...in a population sense, I know none of you would ever want to get Pak 88s against literally-only-infantry) because the first side bought 10 Grens while the other got 10 Scripts. A manpower income advantage would allow a player to get the same quantity of units faster, a population advantage would allow a player to
always have a greater quantity of units without losing them
like Vance Stubbs on Baneblades more often so the others' units better kick proportionately more ass.