Riflemen are mediocre and usf got no elite infantry.
Echelons are for emplacements builder and building holders.
Mortar doesnt have range and never hits its target.
So your stuck with mediocre infantry, mediocre weapon teams and captain tier sucks.
Late game tanks are just medium tanks which perform mediocre.
AND the micro required to play usf is insane!
Commanders needs to carry usf and if you pick the wrong commander you lose the game.
So either you steamroll them early with liteunant or you lose late game, going captain is suicide.
My thoughts from playing usf in 2v2.
Echelons are great for putting zooks on, building wire on cover, sweeping for mines, and for harassing enemy points.
Mortar has good range post-patch, and has same lethality - meaning it's quite lethal.
Riflemen are very good - as good as Volks in early game, better than Grens in early game, and when equipped with either 2x BARs or BAR/M1919 in mid-game, they are the best infantry in the entire game (especially with vet). Other weapon teams are good too - including PACK Howi, which has quite lethal with its accurate barrage, and the MG is of course fantastic - high damage, good suppression. Captain tier overall is very nice - the AT gun is fairly decent, and has great abilities (range boost and AP shells), and of course contains the PACK Howi and Stuart. I love the stuart and get it to Vet3 in 75% of my games. Of course Captain is nice too - free unit with your teching.
Late game tanks are nice - sherman is a little lackluster, but the Scott excels at killing infantry, and the Jackson is the King of allied tank destoyers. In the supreme late game, 3 Jacksons is the best thing you could ever ask for for fighting every kind of axis tank.
The micro to play USF is different I'd say. While axis relies on good MG micro and anticipation, USF requires good unit splitting and also anticipating where MGs are. Differnet micro, but I wouldn't say harder.
Commanders don't carry the USF faction as much as suppliment. I go Infantry every game so I can build early sandbags, get M1919s ASAP, and the Priest is very nice at eliminating campers, forward OKW trucks, or shelling HQs on smaller maps. Thankfully, there are many other good commanders if your mate will get arty himself, including calliope, pershing, airborne, and recon company. I've seen all of them used with great effect.
In conclusion, riflemen are strong early game, and ideally you should win the early game. Mid game can be a bit tough, but if you micro and play well, and can survive till late game arty, Jacksons, and vetted Riflemen with M1919/BARs, you're in a great position to win.
PS Captain is not suicide, I do it 100% of games when I play 2x USF
PPS I've beat many good teams while playing 2x USF, so I think I know what I'm talking about (including Brosras/Antaria, Brosras/Antavrick, VonAsten/Crossfire, Sully/Stark, Theodoseos/Thanatos, etc...)
Next time you are losing as USF, please do not just come on the forum and flame about imbalance like most other people do. If you actually come on here with the mindset that you need to improve your gameplay, rather than blaming the faction, you can improve.