Good question, personally I just don't like the (intentional) decision that was made to make it an all-ranges upgrade. Combined with flame nade it means that Volks can 1v1 any enemy squad, either by (a) closing the distance and flame to force the enemy to move around, or (b) waiting for opponent squads to close the distance, dropping models on the way and still winning up close (+flame +sandbag, usually). Basically they can turn any situation (offense or defense) into a favorable one and have consistent DPS output the whole time.
I would rather have a different upgrade that has even higher DPS, but is focused on either short or long range, so the OKW player has to actually think about positioning rather than just running stuff around from different angles and spamming nades.
while i do agree that the all range upgrade is bad and they would be better if they had all mp 40 or a LMG like weapon, STG upgrade is literally a worse bar upgrade, 2 STG deal less damage than bar (yes bar upgrade damage at all range too) and they occupy 2 weapon slot
if stg are op bar would be OPOP