That's one way to think about it. Another way to think about it is that WW2 was two separate campaigns: one between all the powers you normally think about, and the other just between Germany and Russia, an entirely-optional war that likely wouldn't have begun if Germany hadn't decided to start it. It's not really that Russia was aiding the Western powers in a single fight; it's more that an independent, simultaneous Russo-German conflict starved Germany of the materiel it needed for its other campaign.
See also: https://nationalinterest.org/feature/what-if-hitler-never-in...