*sigh*
It's an entirely different thing walking with your weapon already steadied against the shoulder compared to running with your weapon beside you in one hand or both hands not readied.
In the first case all you have to do is raise the front end of the weapon up a bit - of course this can be done fast!
And this is how it should be animated in-game. This is how every soldier, police officer, and gun enthusiast I've ever talked to has been trained, and it's pretty obvious why. It's lightning fast, and very accurate.
In the second case (which is the one that is what happens in game) you have to first change your grip to hold the weapon correctly, then align it with your body, stabilize it against the shoulder, align the sight with your eye and with the target, all this takes just a fraction of a second which is wrong, it's not possible to do all this so fast.
I agree that this is next to impossible, but I also think that the animations in the game do a pretty bad job of relaying how the actual soldiers used their firearms. Even if the Axis soldiers were trained to carry their guns in one hand (for reasons that are mystifying to me), the Soviet soldiers all carry their guns in two hands, meaning they could easily snap to ADS without changing their grip or shifting the gun. I understand why the avatars in game are modeled to carry their guns in one hand (long range IFF, predominantly), but it is kind of an immersion breaker.
Also, in the game you can run full speed, stop, aim down sights and headshot someone at long range in the blink of an eye.
Not with any sort of consistency. Sure, it may happen once in a while against an exposed or immobile target, but it's hardly the norm. More often than not I sprint for one reason and one reason only; to get to cover. I never let go of the shift key until I feel I have reached a safe location, and then I set up and return fire. The reason for this is simple. It takes a lot longer for me to stop, turn, find my target, aim, and shoot someone than it does for them to line up their shots and shoot me. Holding still only makes their lives easier.
As I've said before, there's no accounting for player skill. If the other guy shoots at you three times, misses all three times, and you manage to stop and shoot him on the first try, well then he just sucks/you're just good. Any decent player would have put you down before you even had time to ADS.
Those real soldiers would not pull that off in nearly the same time even when walking. They're able to get the weapon up fast, but they're not going to be very accurate that fast, but then again it's not needed when you only have to hit someone 5-10 meters away.
Again, not from one-handed carry, but real soldiers in CQC wouldn't drop the weapon down to one-handed carry. If I had to guess, TWI animated the Axis soldiers to one-handed carry so they would be identifiable at range, not because it was realistic. Shame on them, but I see why they did it. Silhouette is the most easily identifiable thing in a video game, and it's important to give the Allies and the Axis different silhouettes so you can identify them from range.