We do not think there was a struggle between capitalism and communism across the twentieth century. For us, communism never ended in that century because it never arose there. Our conclusion is built on the fact that communism –if understood as a distinct, non-capitalist class structure– was neither a significant, nor a sustained part of the history of any of the nations conventionally labeled communist.

emphasis mine, their entire argument is based on the fact that the USSR lacked the class dynamics of communism, thus weren't communist.

[–] Cowbee@lemmy.ml 5 points 3 hours ago

Nobody, not even the USSR, claims they reached upper-stage Communism. They were Communist in ideology, and Socialist in structure. Their argument is a left-anticommunist argument against a claim nobody made.