As of 2024, with a few decades more of historical perspective, I argue that they were in fact adaptations of socialism.

Russia was in a particular state of social, economic and political (under)development, with its own agrarian feudal system, an absolutist monarch, the Orthodox Church, an Asian Empire, etc., and on top of that the socialist revolution happened earlier there, even if only slightly.

Fascism and naziism are adaptations to different societies of the same basic doctrine and system, as is the current Corporatist State in the West almost 100 years later.