Suppose Barbarossa does not go off but the Pacific war does.
You mean, suppose we imagine what we've been talking about for the past 6 pages?
Where does it profit Stalin to torque off the one Pacific power that can successfully damage the CCCP?
Under Soviet doctrine the capitalist powers needed to bleed each other to exhaustion. If the Japanese and Germans were the weaker side, then it was worth it to the Soviets that this weakness would be corrected. Ideally, the Germans, British, Americans and Japanese might merrily be killing each other for 10 or more years, sinking into exhaustion and making way for glorious socialist revolution.
Would it not be better to let the Americans hammer the Japanese, then take Manchuria (which Stalin nearly did anyway, RTL.) at the endgame, when the Americans are about to execute Downfall? The Americans have cleared the way and made it a Russian east Asian walkover. If Stalin supports Japan, then FDR and then Truman and whoever follows them will have a big permanent bullseye on Moscow.
Best case scenario for Stalin is, while maintaining formal neutrality, to make the Japanese so dependent on the USSR that it falls into the Soviet orbit and goes communist. If the US is going to win the war, then the second best scenario is to launch a massive offensive at just the right moment to capture not only the Japanese empire in Asia, but as much of the Japanese home islands as possible then turn the Soviet sector of the Japanese home islands into one of them there socialist paradises.
It is not in Russia's interest to support Japan, or let anyone else attempt to do so, and that is where the whole thing about Europe helping Japan really falls apart. The notion is ridiculous.
I am amazed by the almost fantastical ideas about how the Soviets would express their interests if not pinned by Barbarossa. Suffice it to say I think you are radically more optimistic about Stalin's enthusiasm for American post-war global domination than I think he actually was.