Socialism, by definition, is democratic workers' control of the means of production. A socialist dictatorial state is therefore an oxymoron.
If the state itself is controlled by a violent maniac (Stalin, Mao, etc.), and the state owns and controls every aspect of society, including the means of production of course, then there is simply no logical connection to socialism.
The USSR and China claim(ed) they are are democratic and socialist states. The "democratic" part is obviously a lie, and was ever since the beginning, since Lenin stole the revolution - and everyone of course knows this. Why then do people believe the "socialist" part?
There was a running joke in communist countries on this subject too:
There was once an important communist dignitary who was treating a sick cow. After the cow died, he said: "What a shame, I had so many more ideas to try!".
This isn't a changing of goalposts, it is simply ignoring obvious lies and propaganda from a regime famous for its lack of regard for the truth.
The Soviets (factory committees) at best held some sway during the early days of the revolution, before Lenin seized power. By the time Stalin replaced Lenin they were long since just a propaganda tool, hollowed out of any democratic control whatsoever and turned to a simple bureaucratic management unit entirely controlled by the party hierarchy.