That's why there's been an entire century of revision to that model to incorporate more democratic forward values
How is a representative election every 4 years in a system where mass media are owned by the capitalist class more democratic than the ideas of Marx? The Soviet Union started out as the name implies, as a union of republics in which soviets, or worker councils, had the decision power. The fact that international interference and civil war (such as 14 countries invading the USSR militarily and many more sponsoring the tsarist loyalists or the anti-revolutionary Mensheviks) didn't allow for a high degree of work democracy without extreme risk to the stability or the country, has more to do with the material and historical conditions of the USSR than it has to do with the ideas of Marx and Lenin.