The fact that bazookas cost the same as shrecks says it all.
Also, show me a replay where an AT gun reaches vet 2 and stays alive to be useful.
Well not really. The schreck is always bundled in some way which means they come at a small discount like the T34-85 dual call-in. If they came separately their price would be more like 70 munis.
That being said they are probably twice as effective so I think the balance is still skewed. The us really needs the bazookas to be better. They have enough light vehicle counters, they need help dealing with tanks. A damage buff or pen buff would be good.
As for the at gun, it becomes really good at vet 1 with its ability which it gets pretty fast since its pretty cheap. The only thing it needs is a pen buff for the at rounds. Even with the ability on it has less pen then the other at guns. It makes it really hard to fight heavy tanks even if you did everything right.