When you've got allied base infantry at 280 manpower, you're talking a significant difference of anywhere between 90-150 manpower just to field your first 3 squads, not including the already heavy hitting first sturmpio squad you get compared to REs or Soviet combat engies. That's a 10-15 second head start that OKW gets on you from the beginning, snowballing fast.
Makes no sense to me, OKW starts with much less mp to make up for the sturm high cost, so the starting advantage totally depends on how much sturms can make the nemey bleed in the single small timespan where it's actually a worthy cqb squad.
Also all infantry squads but unupgraded cons and late game penals perform better. We can debate on performance/cost...but outpermorming allied WFA infantry ? Not even against a single bar/bren, especially with the low combat veterancy bonuses volks get.