I like A.Soldier rework idea. Could you skip T1? I mean going from T0 to T2 if no support weapons are needed?
Also doctrinal units "upgrading" non doctrinal ones, seems original.
My best idea to give USF a proper rework, is around Lt, cap, and mayor. Maybe making them more important yet fragile squads, some new skills could help too.
Yes, most of my ideas are based on the CoH American Army which was a better execution in my opinion.
There you could skip tiers as well which made the system flexible in that you only needed the barracks or weapons support center to unlock the supply depot, which own it's own unlocked the Motor Pool and Tank Depot.
Cut the Supply Depot out of the equation as well as the barracks and you would have something similar to what we have right now.
And yes the "upgrading" of vanilla units is also taken from the Tank Depot where you had Smoke Shells unlock for the Sherman as well as the 76mm up-gun, the M10 however had no such upgrade, instead it could be replaced by the M18 Hellcat in the reward units tab if you had Tales of Valor.
And lastly, officer units in CoH were 1 man, and I would say the British system at least made them exactly what you want, lots of utility (stat boosts for other units for example) but extremely fragile (because of 1 man squad). The German officer was also in sort of the same situation altho I prefered to have him in my base boosting production, similar to the USF Captain's building oversight ability, I think that's where they got the idea from but it's a waste to have a combat unit like that hang around the base in my opinion so it's a worthless ability really.