The faction isn't designed to punch you in the mouth with elite infantry. You have weapon upgrades for your rifles to help them scale into the late game. As has been mentioned before, paras w/ m1919s are amazing, arrive before obers, can deploy anywhere, and reinforce in the field at the same cost as rifles. The infantry commander basically turns your rifles into elite infantry at the same cost of an LMG or BAR.
An argument could be made that the strength of rifleman (and the USF in general) needs to be a little less polarizing, with their early game toned down and their scaling increased, but this would take away much of the flavor of the faction. In 1v1s this creates a really fun and interesting dynamic.
In team games it is much harder to really push your early game advantage, and many players feel frustrated when playing the USF because you really can't afford to sit back and let the battle come to you. The clock is ticking, and you need to win early. The USF is not an easy faction to play, and I think giving them units that deliberately fill the intended holes of the faction is going to be bad for balance and design. Giving the USF a Pershing would be insane, because no other faction has access to such a versatile T4 to back it up with. Just as giving the USF elite infantry would be over the top because they already have so much flexibility with their rifleman and their upgrades, it would feel redundant imo.
I dont know why u brought the pershing up? but ok. I think if USF get rangers or something it should be similar to the captain. the captain CANNOT pick up any weapons unless a bazooka man is lost. And for regards to the pershing, I think it would be fine to add. If relic reworks ostheer t4. Which is pretty usless in 1v1