Memes

it’s clear they wanted to keep him [Hitler] on a leash and have him serve as a first line of defense

This is basically the thing I'm arguing. The Soviet Union was never an expansionist project in the military sense (they wanted to spread the revolution abroad, such as by assisting the Republicans in Spain and giving weapons to the Vietnamese in their anti-imperialist struggle), never projecting their military force outwards except because of serious provoking by third party foreign actors (such as in the case of the funding and arming in Afghanistan of radical theocratic militias by the US).

The fact that all of these western leaders talk of the USSR using the Molotov-Ribbentrop as an "odious but necessary defensive measure", proves to me that they understood that the USSR wasn't something they needed to be militarily defended of by a weaponized Germany acting as a buffer, hence that can't be understood as Germany's role in the situation in my opinion.