First: i think they cost alot of manpower (340). I know there price got dropped from 360 to 340 but 20 mp isn't a very big difference.
Second: they die relatively fast on the battlefield vs rifleman but do a little bit better vs conscript. so i think an armor buff isn't a bad idea to do there high mp cost.
third: the only way they are truly effective is as an at unit support alongside a pak43 and p4's. But the panzershreck cost 120 munition so i would have to wait a while before i get that much munition since i have to pay 60 munition for the medic bunker and also get lmg's upgrade.
Those are the problems i have with the panzergrenadiers they aren't that effective on the battlefield do to there high mp cost and there low armor. so they are next to useless

that's just my opinion on the panzergrenadier.