Do marxist really belive that if hitler wasn't born, 6 millions would still be dead at the end of world war 2?
Marxists reject the idea of greatman theory because to argue that Hitler was directly responsible for all the atrocities of WWII is a somewhat reductive analysis. Yes, Hitler gave the order, but who pulled the trigger? Yes, Hitler gave speeches, but who gave him the microphone?
Hitler was the face and the commander of the Nazi regime, but let's not kid ourselves into thinking that he was alone in building the Nazi war machine and enforcing it. Alongside him were others who shared his genocidal aspirations, who (if we are to deal with hypotheticals) could have also followed suit and did what hitler did.
Alexander the great was nothing without his army. It's due to the fact that most historians portray and write history as more of a story often with a lack of materialist analysis that we get these greatman theories. There are probably hundreds if not thousands of people in the world who could, if given power, be like Adolf Hitler, but they lack the connections, resources and men to do so.
>That operation barbarossa would be a failure?
Again, a hypothetical. But at the end of the day, Babarossa was a failure.
>Or that if gorbachov wasn't born the soviet union would still fall?
Again, a hypothetical, at the end of the USSR fell.
>Or that if trotsky succeded lenin the USSR would be the same thing as with Stalin?
Again, also a hypothetical. We can see the ideological differences in both sides, but we can only speculate and imagine how the USSR would have changed based on these policies being enacted, which again, leads us to analysing history as more of a story and have us try to analyse material conditions which may or may not have arisen based on said policies.