If the SU-76 was supposed to not be shit, Relic would have made it not shit. See how this line of argument works?
Since I know you're a little*... mentally incapacitated I will try to make it as simple as it can possibly be so even you may have a solid chance at comprehension:
Balance is not the same as game mechanic just like apples are not oranges.
Bad balance can be a source of bad mechanic, but not the other way around.
Comparing or even using that as analogy is simply stupid.
*vast understatement