"It's a simplification, but historically warranted, in the sense that the USSR was created explicitly with the end-goal of leading to a communist society as described by Marx/Engels..."

IMO, it's not very fruitful to study the ideas of Marx/Engels together with the soviet union. Soviet union was a military dictatorship that used the communist story as the replacement theology for their domain.

Sure, there were the true believers who ate up the dogma but I'm pretty sure most of the soviet leadership were pragmatic revolutionaries who just wanted power. They needed to replace "the story of the czar as a loving father" with the story of the communist agenda in peoples minds.