"Really existing socialism" of course meaning "a system wherein workers have zero effective political power."
Just because it's true that the ML movement was an essential part of decolonialization, and because it isn't true that the USSR was some evil empire, doesn't mean that the ideologies that underpin(ned) those societies aren't deeply flawed.
The USSR was not an evil empire, no, but the political structure of a hierarchical, command-based politic lead exactly where critics said it would lead. The "ultraleft", as you call them, including Luxemburg and Anarchist communists warned Lenin exactly what would go wrong in the USSR, and Lenin did not listen.
That's why Lenin is a counter-revolutionary by deed if not by intent. By his actions, the power of the people's and worker's soviets were shattered and replaced with corrupt bureaucracy.
Also, hey, go tell a Tartar, Kalmykk or other displaced ethnic group who were victim of Stalin's genocide that he wasn't a deranged butcher. Maybe if you survive you can tell me what you learned.
s!
We want our slop but we can't afford it
Give the people what they want!