Technical correction for historical accuracy: the USSR, PRC, etc. never called their countries Communist, but were led by Communist parties that, by their own words, were attempting to build Communism. Marxism-Leninism posits the strategy of building up the productive forces via a transitional Socialist stage before reaching Communism.
I’m not an ML myself, but it’s important to understand the distinction. That’s why the Union of Soviet Socialist Republics was not the Union of Communist Republics, because even by their own admission they were far away from Communism. This is completely separate from how effective or ineffective we may analyze them to have been at achieving this stated goal, that’s an entirely separate conversation that again, I’m not an ML and am not interested in arguing.