I disagree. Russia will not fall at all if Japan is at the gates of Moscow because Germany will be at the gates of Berlin.
Actually, the BEST game I ever had was when England went balls to the walls against Japan by landing in Archangelsk, through Russia and into Novosibirsk while Russia pushed into Europe and America worked on Africa and landing in S. Europe (as defined as W. Europe, S. Europe, Balkans and Ukraine.)
This maximized Russia’s income because England liberated land while Russia conquered land and it conserved Russian armies by not forcing Russia to trade with Japan. This allowed me to get 30 Armor with Russia, and if Russia is strong enough to have 30 armor to throw back and forth across the board with impunity (or very near) then it’s game over for the Axis.