http://en.wikipedia.org/wiki/Assaul...:_Maschinenkarabiner.2C_Sturmgewehr_.26_AK-47
The Mkb was part of the first generation of dedicated assault rifles. Large magazines, select fire, high penetration, and excellent accuracy out to the average combat ranges (< 300m). It and it's cousins (the StG 44, etc.) sparked the arms race that revolutionized small arms like never before. Suddenly, one green soldier could put out enough firepower to match an entire squad of elite bolt riflemen, and you could have an entire squad armed with these things.
We're running into that same problem here. A significant number of Germans can put out enough accurate, high-penetration firepower to match 3-4 bolt-action riflemen each, and the Ruskies have no counter to it. If they gave them AK-47s, then it would be a bit more fair (though the AK is superior to the Mkb in many respects), but at the moment there is no counter.