People are either ignorant or unaware of the fact Russia also invaded Poland when Germany invaded. They had also invaded Finland.
The western allies saw them as useful idiots. More of a “the enemy of my enemy is my friend” kind of thing.
As far as the west helping Russia defeat the Germans, Russia had stopped the Germans at Moscow in Nov 1941, before the USA had entered the war. Once the USA entered the war against Germany, AND Germany had failed to rapidly defeat the soviets, their defeat was pretty much a case of when and not if.
Things might (emphasis on MIGHT) have played out differently in Europe if Hitler hadn't shown a Putin like level of tactical brilliance in his decision to declare war on the US.