Why should germany be ready to push into Moscow on turn 5? The allies are dropping of units into Karelia faster than the Germans can build up. Germany is lucky to hold out until round 6 never mind being the one to cause the russians to retreat to Moscow. Germany’s goal is to stay alive and threaten Russia as much as possible to limit what the allies can throw against Japan.
By turn 5 the allies have had 10 transports pumping units into Europe. 20 allied units plus airforce can hit W. Europe, Germany or E. Europe by navy alone, no way Germany takes Karelia and you can’t threaten Moscow as Germany without Karelia.