It was not a dictatorship because it did not produce the material results you would expect from a dictatorship.

If it had been a system in power of a few people against the vast majority, as was for example monarchic feudalism (the state immediately before the USSR, the Russian Empire, being a good example of it), you would expect vast inequality leading to a two-class system with vastly different life metrics, wealth, and a degradation of the rights of the working people.

However, the Soviet Union had the lowest wealth inequality the region has ever seen, the highest earners were the highly trained professionals (not policitians as you may have been led to believe) and the salary difference were perhaps at most tenfold; access to healthcare was universal and free, as was education to the highest level, pensions for retirement were universal with men retiring at 60 and women at 55, homelessness was abolished and everyone had access to affordable housing (3% of monthly income on average), and everyone had the right to a job making unemployment nonexistant.

A system producing these outcomes is not the result of 4 generations of "benevolent dictators" from 1917 to 1991, it's outrageous making such claims.