What do you even mean by scaling, by your logic the only scaling for Grenadier is MG42 ?
If we look at pure bonuses from veterancy, USF and SOV mainlines are scaling way way WAY better than their axis counterparts and Infantry Sections build on to an insane base value.
And finally, if Grens and Volks are being "upgraded" to Obers and PGrens, so are Concripts to Guards and Shocks, Infantry Sections to Bren Commandos and Rifleman to Paras and Rangers.
If we look at weapons, both UKF and USF can field double guns on their units, which combined with better "veterancy bonus" infantry makes them basically elite infantry. And yes, in team games USF infantry is supported too with its SOV allys Katyusha or UKF Off-map barage.
Commandos and paras and shocks and guards are stock...
I'm not talking about veterancy scaling. Neither am I talking about pure mainline scaling.
If looking at mainlines only. Yes, allies win here (with exception to conscripts until 7th man).
However, in teamgames, you'll see a lot of builds which deviate from the usual 1v1 builds.
Eg: Most of the builds I've seen playing vs OST are: double MG42s with double pios. Light vehicle and then 3-4 PGrens.
OKW: Sturmpios, kubel and then one volk squad into vehicles and then 2-3 ober squads.
In 1v1 such builds would usually end up with a loss before minute 15 due to severe lack of map control. But in 3v3+, that's really not an issue.
In the later stages of the game, in teamgames, most infantry engagements are long range. Nobody is stupid enough to go through no cover zone to reach the enemy squad, when there are plenty of killing machines that can stop that halt and bleed you. Nobody can deny that Axis are dominant in long range engagements. It even says in the unit description.
So basically rifles sh** on volks and grens in early stages of the game, but once the game progresses and BARs further amplify the short-medium range firepower, the Obers pretty much eat vet3 rifles, unless they have to close in (eg, you're behind cover and obers don't have any cover to get behind)
Conscripts are weird, not gonna comment the weird scaling of that unit. Pretty sh** until 7th man, then they shine.
IS dominate early on on long range, lose short. Brens do give them the edge long range, even vs Obers but don't really have anything to follow up with. Also have a power spike with 5 man.
Of course, if doctrines are picked, then the situations shifts a bit, depending which elite unit you get (if you get any at all).
Fussies are also in a weird position, but are doctrinal so not gonna comment.
In all the games I've played with USF, if I've won, it's been in first 20 minutes of the game most of the time. As the game progresses you find it more difficult to deal with the obers/PGrens. Even if you go trading with them, a werfer will displace you (or stuka). If you try to do the same with a pak howi, good luck. Not to mention how rifles are quite bad in snaring (due to the long animation, and God forbid the snaring unit is killed, the animation starts over).
I'm not denying that the ally infantry is strong. It is. Allies have stronger mainline infantry that is more versatile, which is exemplified in 1v1s where it's quite important. But in 3v3+, mainlines are not your bread and butter which win the game, only to cap. Elite squads shred infantry, mainline or two cap, while tanks battle it out with support from rocket arty.