Regarding USF I'd personally make Riflemen 10-20MP cheaper and add those (based on standard 3x Riflemen strats) spare 30-60MP to the BAR tech. This way USF can field infantry as fast as OKW can in the early game, while their scaling costs/timing remains the same as it is now.
Infantry Sections I'm not sure, I'd probably agree they're fine early on. I'm not even sure IS are really the problem for UKF. It might be worth experimenting with only one Bren slot and add a moving accuracy bonus to the Bolster tech (bringing it up to standard) so they can actually properly attack stuff.
Reducing Riflemen cost isn't going to change anything. There are two issues on OKW-USF matchup
-OKW start with 100 Manpower more to mitigate the truck cost added recently. But this 100 Manpower is actually used to build a 4th volks squad early game.
-USF Gameplay is balanced around strong Riflemen but capped at 3+Lt or 4+Capt. Whenever it is the 4th riflemen or the lieutenant, the squad hit the field much later than the 4th volks squad.
If you look at both at the same time, the problem is quite evident and not to forget that additionaly:
OKW start with a Sturmpio and USF a RE squad.
OKW Volks can build sandbag while Riflemen can't
Once first truck is call-in, volks Access flamnades
So reducing riflemen cost isn't going to change anything, you can't build more of them or
bleed like a stuffed pig. So what for, an early mortar? isn't going to counter OKW non-static play, Volks can build another sandbag if you target the first one.
Elchino7 already gave the best solution here: removing this 100 Manpower for OKW and reducing the truck cost so the OKW player can't build the 4th volks in a raw.
In addition, putting sandbag behind vet1 would also do great for the balance.
Soviet could also use of a nerf for their penals, removing some of their initial stat and putting them behind vet1
Ostheer is already going to be nerfed with the doctrinal changes to mobile defense. I don't think that Stock Ostheer is superior to Stock USF, it has always been a doctrinal issue since they forget to apply all doctrinal nerfs to Mobile defense last year.