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Meanwhile ost gets pgrens nondoc. They're not precisely cqc inf but they're very cost efficient if you use them right, and don't require muni upgrades. Allies don't really have any nondoc analogues and brits and usf only have 1 combat infantry squad nondoctrinally. Asymmetric balance I guess. Volume doesn't really matter either since you only get to pick one commander anyway.
Ok. Lets go slowly step by step.
USF and UKF got 1 combat inf nondoc, thats true. But they also get more than 1 weapon upgrade (bars,brens,zooks,piats) and on top of that doctrinal buffs, making them very versatile if you compare them to their axis counterparts. Its not a disadvantage from a realistic point of view, its a trade off. Also they both come with T0, But only OKM has volks on T0 to balance axis/allied.
Now, about the cost efficiency of a well used squad, that sentence can be applied to any squad and I mean,
any squad, even pios can displace any HMG if it is outside a building and it got flanked, combat engineers can secure a VP without loosing too much MP, and so on. Some units punish harder than others for such good plays, maybe that was the point you wanted to make and it would be pretty accurate, since once pgren are able to flank they do wreak havok in the frontlines and speciialy on team weapons, only full hp mainline inf can repel them. IMO Pgrens are not cost effective per se but only if a nuke grenade gets a wipe.
And finally Allies may not have nondoc analogues to pgrens and specifically not at the same level as pgrens, but UKF RE, a couple of conscripts squads and USF riflemen after performing a good flank can do the same job to repel team weapons and hit frontiles in a weak point.
Even if you add to the mix smokes, you could argue that results wont vary too much, the shock value of the bundled grenade is awsome on pgrens and that could be its best part, but all the prior mentioned troops with assistance of smoke are able to breakthrough at some degree. Again we talk about good plays and using cover each time its available. Therefore Pgrens dont stand in any of the 3 points you made.
Edit: IMO Asymmetric balance favours no one, but those who do adapt in the battlefield