How do the issues you describe with USF not apply to sov as well? because they have access to heavy tanks?
SOV possess a lot more utility than USF when in comes to displacing or killing support weapon teams including HMG and ATG.
- Sniper forces the unit to immediately move or risk squad wipe.
- Mortar is significantly cheaper than pack howizter and provides more reliable high angle fire. Not to mention it provides smoke for free to cover tanks if your not sure where exactly to barrage.
- Zis-3 has the potential to be a threat with barrage.
- Access to on-map artillery is more readily available to SOV via T4 (katuysha/SU-76) and doctrines.
- Both T70 and T34 can easily survive from a pak40 as long as you do not over commit. T70 also has recon run which can more easily determine the exact location of a pak40.
- Heavy tanks can destroy pak40 outright.
There is probably even more reasons that I can't think of, but yeah SOV have heaps to deal with it. USF has few that does not result in a risk in losing MP and catching the pak40 out of position for an easy flank with infantry/armour. The chance of pak40 being poorly placed in the hands of a good player an a high LMG gren army (more vision control) composition is low.