Because the power of the PTRS is the alpha damage. Walk up, instantly kill several models or make a crew weapon disappear then pull back.
The DPS is shite because it has a long cool down and reload, but if you volley half his army to death in the first shot who cares about reload?
Jagger infantry can do the exactly same thing. If it's fine on one unit then it's fine on another. DPS stands for damage per second. PTRS have abysmal reload which makes their DAMAGE PER SECOND bad.
Ability to evaporate support weapons is completely different matter and that's should be changed. I don't like that horde of Cons can render any kind of weapon team play absolute. I ma not sure however how this can be fixed due to engine limitation.
The other way is to make PTRS decent AT weapon at the expense of their AI capabilities. Going back to PTRS being useless it's not an acceptable solution.
With all fairness it's only one commander that renders PTRS OP because it makes them too common. Maybe adjusting the commander is enough to deal with the problem?
Make Conscripts pay more for their PTRS rifles to limit the number and distribution through out the game.