Yeah, "but it wasn't real Socialism/Communism/Marxism" comes up as an excuse by leftists all the time. Of course it wasn't - because "real Socialism/Communism/Marxism" is impossible.
Now, that was never going to happen, because of the iron law of bureaucracy - states only ever consolidate their own power so Lenin's plan was doomed from the start. But the USSR was never socialist.
I'm not sure what you think is impossible about socialism, because if we were to legally replace corporations with cooperatives, which is not a huge jump in terms of economic law, that would be market socialism. Its happened before (briefly in the USSR before the consolidation of the bolsheviks in power for example, for example in the meaning of the word "soviet" itself) and cooperatives work perfectly well as an industrial unit.
Coops based on voluntary participation are entirely compatible with capitalism, you can already set up a coop today in capitalist countries. Socialism is not voluntary, it forces everybody to participate. It is the most exploitative system, because everybody is supposed to only work for the common good, not for themselves. It also sets the wrong incentives which is why it usually ends in misery.