Its not a design fault. Ost has two tiers of infantry - grens and pgrens. Somewhat like cons and penals for soviets. If you want to use your lower tier units as strong mainline inf you need to to make it a dedicated choice (using a commander). Same as cons can't keep up with other mainline inf. Ost has other great tools to win fights that everyone is forgetting and want to make them strong in every aspect.
This is theory is simply flawed. Penal can be the backbone of your army even stock. PGs can not simply because they come much later.