Well, conceivably the effect would be cumulative. Russia was not the monolithic giant with endless supplies of men and material that it is sometimes portrayed to be. Just like any nation, the USSR had its limit - as has been discussed recently in relation to Lend-Lease. In 1941, its breaking point was surely smaller than in the years after.
It can be argued that had Japan applied pressure in the East at that critical time, allowing Germany to take Moscow and the other major cities and push the Russians behind the Urals, they're capabilities would largely be diminished.
Surely Stalin may have been able to use the vastness of the environment to elude total defeat for a time, but even with as much Russian industry as he was able to move - being trapped in the middle of undeveloped Russia would have him strangled for resources and the ability to launch offensive operations.
In any event, I believe better coordination between the two powers leading to a Japanese attack on Russia would have been a far better decision for the overall Axis effort than bringing the US into the war. Of course, taking their entire fleet into the middle of the Pacific and scuttling it would have also been a far better decision than bringing the US in, so hindsight is 20/20.

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