At least for me, I have no problem with any weapon/upgrade as long as I can reasonably imagine a story behind how my character managed to procure it. I can easily imagine my embittered veteran "trading" weapons with a new recruit he simply sees as fresh, dead meat or "appropriating" a new rifle in a rear supply area. And for the Soviets--yes, I can imagine a Russian unit commander requesting a better machine gun for his best soldier, an Order of the Red Banner-winner notorious for killing over forty enemy infantrymen. Given the cult of weapon expertise Chuikov directly sought to inspire in his men, I can easily see a deserving Red Army soldier get rewarded. It's fairly well-known that Mr. Vasily got to play around with an anti-tank rifle for a time before he decided it was too inconsistent for sniping. Who's to say that a more lowly but effective trooper wouldn't get first pick?
That's not to say that there's a mail-order system in place for both sides that allows soldiers with x amount of kills to get weapons air-mailed out to them. They just have methods of getting their hands on what they want, regulations shmegulations.
It's an interesting idea, and I'm not all that inclined to look at it negatively. At least your weapon doesn't get tiger stripes on it.
Stalingrad was a battle fought on an intimately personal level between both sides, with moments of unspeakable horror and brutality but also larger-than-life stoicism. I actually think that a properly implemented progression system does justice to that struggle. There are certainly issues with the current unlock/stats system, but it's not inherently unacceptable.
--Ability to select which unlocks to equip
--Limitations on rare weapons/unlocks
--Decrease in the potency of certain stat boosts
And we're golden, in my opinion at least.
This is all just my personal take on things. You don't have to agree with me, and I'm not trying to convince anybody. I just have a vivid imagination