Nobody has made the claim (nobody serious anyway) that they are OP/unstoppable, they are simply to efficient for their cost and they outshine anything else Soviets can make.
Exactly the same can be said about StuGs.
And you're wrong.
Yes, they are effective against low micro blobbers like you, but players who actually have a clue have no problem countering them, just watch Hans games where he uses them, opponents equal to him have no problems against them, therefore its L2P issue, OKW eats soviet T3 for breakfast with JP4 and you can do nothing against it.
Soviets not having to go T4 at all is silly when USF (minus 1 commander) and OKW can't refuse to fully tech. And Ostheer can't get to their T4 (which has no equivalent) in competitive games due to the overwhelming cost compared to other factions tech.
Its also not possible, unless you're closing the game within minutes of getting T3.
Nobody is asking for it to be useless, but 50 range would certainly not make it so and neither would slightly less pen. Would the StuG be able to fight and win? Yes! Of course it would and should considering it costs a fair amount more.
Making it counterable by everything is asking for it to be useless.
50 range would do exactly that, unless you want to decrease cost as well to lower then pre patch level.
Turreted TDs have that kind of cost as well as amazing vet abilities and actual survivability/mobility.
Maybe they are not a problem in 3v3 and 4v4 but in the competitive game modes they have basically put a bullet in Soviet T4's head. And dealing with SU-76's require far more effort then using them does especially for how much/little they cost.
They aren't a problem in 1v1 or 2v2 as well unless you're scrub.
JP4 shuts down dead whole sov T3 single handedly.
Pak/P4 combo also makes a short work of SU-76 spams.
Protip:
Paks are not emplacements, you can actually move them when you hear the long ass cooldown inaccurate barrage.
In short:
You being unable to counter this unit with clear and exploitable weaknesses that is countered by simply adapting BO and not being blind pidgeon does not equal to everyone not being able to do so.
Watch streams/replays of players who rely on something more then sturmofficer blobberino into panther into JT and don't rely on that tactic to counter everything and anything.