The purpose of a system is its outcome. If the elections only ever produced comically landslide victories for the ruling party, then that is a guarantee of a sham election.

Even if you assume every Soviet voter was a full-on true believer Communist, you would still never have such outcomes in fair elections. You would end up with multiple communist parties, each practicing a slightly different flavor of communism, vying for the vote.

Any voting system where the ruling party endlessly wins overwhelming victories is guaranteed corrupt and a sham.