By the time late game hits and you have vet 5 Volks running around your problems are probably going to be a lot more to do with the heavy armor running around the field and not the Volks.
Every army has a core. That core usually consists of core, basic infantry.
The problem is when your core, basic infantry eventually vets up and has -49% received accuracy while getting accuracy buffs and having a Schreck at the same time.
You will lose if your core infantry will lose out to your opponents core infantry heavily. You will need to counter them with something else then. But there is also armor that needs to be countered too.
And what does your opponent do? He enjoys seeing you trying to counter him in a desperate fashion because he is assured his Infantry will beat yours and you need to invest significantly more units and micro.
Thats an issue. Im fine with Schreck'd Volks, but not with their ridiculous vet bonuses. They need to be toned down.