When you are made to charge across a 100m long square, a rifle will do you more good at keeping the heads of the Germans down or off than an SMG will allot, but lets say once you have established your foothold at the base of that building, you're going to want to go at it with your SMGs against entrenched Germans.
Considering that you can actually give *some* suppresive fire with say a ppsh41 while moving, and the psychology of the situation, and the skill of most rifleman, 1) the Russians only have to really fear the MGs and the occasional good rifleman up to 50 meters, and 2) the PPSH is actually better at keeping heads down at 50 meters.
If you have tons of bullets zooming by you, you think your under heavy fire so you completely hide (generally) if you do not see A) where the bullets are coming from, and B) where the bullets are hitting. If you have the occasional rifle shot coming near you, you think "hey its a lone rifleman, I could pop out my head and probably take him."
What is not mentioned is that the the first case is just a lone PPSH41 shooting super inaccurately at long range. However, in my experience, people will hide in the first case (because like I said, they think they are under heavy fire) while in the second case they will often expose themselves even more, so they can find where the rifleman is, and kill him. In reality, the SMG would never kill at that range, and the rifleman easily could (even before the person exposed themselves more.)
I will almost always go rifleman, so this will be no exception. However, between smoke, grenades, and pubbing MGers/Rifleman not being what your used to, I think you will quickly find the SMGs will probably dominate. I'm guessing so far mostly clanners have tested this map. While I enjoy Clan matches (and indeed, have fought with and against CoreNA in clan and IC matches), I'm a pubber at heart, not a clammer. I do not disagree with those class loadouts, (I see no reason the Russians shouldn't get whatever the hell they want), I'm just saying it will almost invariably not work out as you expect it too.