One thing I will say about the USF is the design of the faction makes them the best at snowballing a very slight advantage into a huge one: free officers, cheap teching, very early scalable light vehicles, weapon racks, high effectiveness of USF units chasing down repositioning units, and the fact that all vehicles except Jackson have some kind of get out of jail free card to further encourage super aggressive play.
If we are only talking about straight buffing the faction with no regards to flavor, I think giving USF a T0 Sniper/Kubel counter with high opportunity cost (WC51) and swapping smoke with AT rifle nades are the only needed changes.
However; that snowball's critical mass is... never really too too threatening. I would argue during the days of Shock Rifle, the Soviets did it better with the IS2, maybe even now to a certain degree with Su76 walls. Sticking within that context, the way to beat USF as Ost was to hang on to dear life, and pray you sustained enough VPs for your opponents USF snowball to hit your proverbial Evergreen tree (Tiger tank + PaK wall) If it really was a true, scalable advantage, those delaying strategies would have failed to the overwhelming tide of cheeseburgers and thousands of rounds of freedom/minute.
I'll further disagree on the point of the light vehicles. They don't scale all that entirely well in the slightest. If anything, with the exception of the M20 as a mine layer, they have 0 equity other than their immediate impact when they hit the field. Every second that passes they become more and more antiquated by the raketen, PaK, or in some cases the 251/2, Puma et. all.
The M15 hasn't really got a joker, regarding survivability, and I would argue that the HP pools are so low, the opportunity to utilize such a joker, like Sherman smoke, isn't exactly a saving grace. The change for the M15 shooting forward is a good start, perhaps given more HP, much like the Ost sniper, they could pose more of a threat against an entrenched player, with the ability to tank more than a faust + PaK round.
Cheap teching certainly is not the case regarding the Major. At 170-90 fuel for... for argument sake, Ost T3, with other opportunity costs such as healing and the vaunted weapon racks, one is either on par, or actually behind in the tech race.
I say... and I curse myself in doing so, so I do so quietly...
take inspiration from PE design and make vehicles in quantity an option to use as frontline units. IE an M20/M8 w.e, give them the combat ability and dps/hp+armor survivability of at least a rifle squad, if not more, for the more specialized and or powerful/more expensive units M15, Stuart. So that we may choose, if we want, to utilize vehicles either as we do now, as essentially mobile support and harassment or as a more monochromatic mechanized army. I think some of the proposed additions of support weapons make sense as well, but I think it should be introduced much like the WSC vs. Barracks in CoH1, The choice needs to be made and carry its own set of unique risks and rewards. A commander should be forced, early on, to either mechanize or play with foot infantry, and be given opportunities in the later stages to hybridize, and then, truly create a snowball of a force, as once one has effectively "tech swapped" it would be very difficult to field enough of a counter to deal with each attacking threat the USF could throw at an opponent.