I agree that there are issues, but I will adress these as good as I can with my knowledge, since some of the issues you describe aren't really the problem.
Early map control and flexibility are USF's strengths. Later on, Volks will outclass them with vet. The key is to get there. Also on long range Volks do win against Rifles very reliably. This is rather a map pool issue. The more cluttered the map, the more you need to be mindful and careful when facing Rifles.
They aren't meant to. Sturms are the key to face aggressive USF in cluttered maps, so I will agree that you need to ambush them. This works great when you manage to do it, but again. Sturms outclass any other engi squad and unlike any other engi unit, can even take on Rifles underthe right circumstances. Their price and upkeep reflects this imo.
I don't believe this. REs are good at long range, but their overall dps is miniscule, so unless there is cover or any other deviation from a "standard 1v1" situation, Kubel should win this reliably.
This is a valid point imo. This wouldn't be much of a deal, if Raketens weren't so fucking unreliable.
But the problem isn't Luchs vs. Stuart timing, since Luchs is that much better at anti inf. It's probably worth mentioning here, that Riflemen AT nades are very good at keeping Luchs away, whereas Volks faust are kinda short ranged and can't achieve the same effect on the Stuart.
Riflemen mines are doctrinal, so that puts it into other territory in terms of balance discussion and I wouldn't quite call it an issue in the general balance matchup. I will agree that Sturm are indeed working overtime right now, because Raketens are unreliable, Volks have no more Schrecks and repair now comes after a little side tech, so Sturms must repair in the meanwhile, but you might need them elsewhere.
OKW's MG34 used to be doctrinal and I still don't see them as essential OKW unit portfolio. It's good that OKW has got asuppression platform, but I like the fact that it's not as good at what it does, since OKW isn't built around having it. Same goes for the USF mortar, which I will adress below.
As with the MG34 for OKW, USF was not supposed to have a mortar. They still got one, after the community tested and agreed to have a light mortar, that was supposed to be a mobile, light damage mortar, that's main purpose was to provide smoke. However, after the testing lelic decided to implement this broken mortar, which will be hopefully changed to be what the community agreed to.
Overall, I would count most issues you listed as invalid, except for the mortar that you mentioned rightfully and Stuart dominance. The Stuart will hopefully be kept more in check when Raketens will be more reliable eventually and in the same way hopefully the USF mortar will be changed in the right way. Keep in mind that my comments are based on my own limited experience and I don't claim to have figured it all out, but after seeing numerous top level players face each other, the key issues with OKW vs. USF seem to be the risky T3-rush tech vs. underwhelming heavy-T1, the overpowered USF mortar and most importantly Raketen unreliability.
From my experience Riflemen do win against Volksgrenadiere at long range if cover is equal not as comfortable as from mid-range but that should be expected.
I also do not agree that Volksgrenadiere will "outclass" Riflemen mid- and late-game. They might close the gap a little but BAR equipped Riflemen at Vet3 are still better then STG-equipped Volksgrenadiere at Vet5 especially because STG doesnt add much long-range DPS which is the only area Volksgrenadiere are decent.
Sturmpioniere are better than any other Pioneer unit because without them OKW would be totally helpless early game.
Riflemen mines are doctrinal but the commander they are in is pretty much meta. Riflemen laying mines all over the map is something that should be adressed. You can´t have Sturmpioniere with mine detectors everywhere, especially not against USF.
At least with the other factions mines and demo charges are being used by Pioneer units so they cant be spammed all over the map unless the player decides to dedicate mulitple pioneer units to mines. Riflemen can engage in their regular primary role: fighting, all the while laying mines. This is bullshit IMO. At least nerf the mines so they are clearly worse then mines layed by pios.
I can show you a replay of Kübelwagen vs RE. RE was in yellow cover, got engaged by my Kübel at long range and easily beat Kübel. Had to retreat it after only killing 1 model while Kübel was at 1/5 HP.