I'm quite sure they are not supposed to have fighting chance vs rifles. Sole reason is, USF have nothing else in the early game, they can't support themselves with snipers or HMGs or mortars, if rifles didn't walked over grens, then mainline infantry spam from faction that have early and wide access to support weapons would be as strong as mainline infantry spam from faction that doesn't have any other option, which doesn't sound balanced in any way.
Whats ur excuse for not giving them a lategame 5 man upgrade?With pack howie,browning,brutal vet and dual lmgs ,plus elite troop call=ins,flamer/.1919 available for usf?
In any case grens are useless vs usf compared to osttruppen/pzgrens.