Ptrs zooks etc are weaker in term of alpha damage potential. That is why they are on sturdier squads and do a bit more vs inf. The shreck esp in larger numbersare a major threat to allied armour able to losse half hp in blink of an eye. Volks shreck blob was the best example of this. And thay had only one shreck each.
All true. But because panzergrens are so much more squishy and it's too easy to waste 340manpower squad just by being sirclestrafed or lose 2 man per sov mine. Very often pack howie or sherman HE round will wipe them too easily.
Another thing is that guards and penals have extra abilities of button and satchel. Rifles have snares and can equip bazookas. Rear echelions are often similarly useful with two bazookas to panzergrens but dont require tech and are so much cheaper. These are just a few examples of real discrepancies.