Personally, the fact that bolshevism and fascism stemmed from distinct political traditions is more humbling:
The fact that tyranny could show itself out of multiple facets of ideological concern (class, national identity, etc.) should keep us aware of its pervasiveness.
I love Mises, but he was notorious for overdiagnosing people and groups as "socialist". Dude even called the Mont Pelerin society a bunch of socialists. His brilliant economic thought notwithstanding, Mises wasn't the most apt political historian.