I understand where you're coming from, and I understand why you believe this is true, especially when you take into account the current consensus among historians and other authority figures on the subject. They generally agree that Stalin and the other figures you mentioned were not fascists.
I disagree.
They qualify as fascists under every metric of the definition, and in abundance. Being communist, or labeling Stalin’s system “Stalinism,” does not exclude it from being fascism. Those labels do not change the underlying structure.
By every measurable standard, they were fascists, unequivocally,
Saying that a totalitarian ultra-nationalistic authoritative and violent regime isn't fascist because they called themselves communists is historically and morally disingenuous.
What a great little technical out for some of the worst people on Earth and in human history to not be called fascists.