Also disagree that rifles dont scale into late game. They can carry two zookas or LMGs and they can melt Obers even. Everything else you bade a very good argument Rifles are simply too strong and game breaking early game.
That's the key, you said it;
early game. They do shine in early game as they are suppossed to win it for the USF, but bazookas are hardly usefull in mid-late game vs enemy armor, for this role RETs can do the same.
Ofc they have useless grenades, 150 mp and 25 fuel to upgrade and 30 to throw one. The animation and the timer is too long, leaving enough time for the enemy to dodge.
For upgrading a rifle with 2 BARs or 2 Bazookas it takes 150mp + 15 fuel and 120 ammo. We agree that the 1919 lmg is too strong, but apart from that and the M7 that doctrine is hardly usefull and more and more ppl are getting Rifle Company which is 10 times better than Infantry Company, while the german infantry can scale well into late-game without a doctrine.
About the strength of the rifles: at long range they do lose to grens, grens with LMG is 240 mp and 60 ammo and is perfect vs rifles as the USF's veterancy doesn't provide as much as the Ostheer and the Gren LMG has insane damage output on long range compared to the BAR. To get a strong rifle you need to spend 280mp and 120 ammo atleast.
Against OKW and Obers it's a different story as Obers have 5 veterancy level and as the game goes on they melt rifles with their stronger vet.
So yeah, their scale is commander dependant (rifle company and infantry company), but apart from that they just become support units to the vehicles as getting all the upgrades it too resource heavy.