I like the idea of gaining 7th men, it sounds like not powerful, but its supposed to be like so. There are many benefit with this upgrade:
Pzgren being later than Sturm but not cost effective, in both utility & firepower. I understand why you think Pzgren should come to the field earlier by setting them available at Phrase1, not Tier2. But I dont like that idea, it makes possible for Ost to skip Tier2 to save 20fuel to rush Pz4, because Tier2 hold ATunits for Ost, makes them can not skip the tech. We know how early Ost Pz4 come compared to Allies core Medium tanks, 20fuel earlier will ruin the game.
It can be fixed by nerfing USF & Brit core infantry. As I mentioned before.
As all factions core infantry have "choice" upgrade. I think its better to give Volk mp40 instead of stg44. To give them the choice between close range or mid-long range.
I did some test in Cheat mod, and I see Volk stg44 can destroy Ost Storm trooper with mp40, it just prove how powerful Volk stg44 in blob.