You highly underestimate the number of units Germany can send. On a G3 DoW, Germany can put 62 ground attack units into Russian territory (not including the Finns, they won’t reach Moscow by G6). Add another 10 for the G3 buy, plus about 3 fig, 5 tac, 2 bmb remaining from the original Luftwaffe, plus probably ~6 more tacs in G4-5 buys yields 88 units set to attack Moscow on G6. A max defense of Russia (only building inf, with a few mech R4 where inf wouldn’t make it into Moscow, and a few tank R5 to spend >30 IPCs), yields 90 units defending Moscow. (this assumes Russia doesn’t put out any blocking inf, but that will probably result in the loss of Ukraine G4, meaning G can put 3 more tanks into the attack) Although Russia has more units, most of them only roll @2, while about half of Germany’s army is rolling @3 or 4 giving an average of 16 Germany units remaining, which would be 14 planes, 2 tanks. This may seem like a pyrrhic victory, but Germany just destroyed every single Russian unit (excluding naval) on the map, and will easily capture the rich Russian south, while using the Russian money to create Fortress Europe, since the US & Britain have to spend extra money on transports to move units across the water.
This also completely ignores Italy, who in the best case scenario for the Allies will have its entire navy destroyed and been forced to stack ground in Europe, which is still another problem for the Wallies.
