I think what they are saying to do in this situation is to leave your ground army near moscow, but try and also surround it while trading territories with attrition battles. Russia won’t be able to lunge because your army will still be very near, but meanwhile you are still cutting at Russian ipcs. 10 inf a round is 30ipcs, and if Germany has all of Eastern Europe then Russia shouldn’t be near that total, even with Korea and possibly some middle east territories.
The problem is, Russia can easily have several dozen (70+) infantry in Moscow, plus whatever else they managed to retreat back there. Sure, Germany can ruin the rest of Russia’s economy. But the fact that Russia can stack so much there so easily makes it pretty hard for Germany to take and hold 8 victory cities, especially considering the fact that in general longer games favor the Allies because of their economic advantage.