Yeah this is the Hollywood version of time travel but in the real world that's not how things work.
Adolf Hitler didn't invent Nazism, any more than Donald Trump invented MAGA, they were just two individuals who were the right moment in history to take the opportunity, have they never existed someone else would have done it, possibly later on, but it would still happened.
Nazism for example came out of frustrations with the rest of Europe over the treaty of Versailles. If you want to prevent World War 2 it isn't enough to kill Hitler, you have to first prevent World War 1, in order to prevent World War 1 you really have to prevent all the stupid little wars that predated it. The number of people you would have to kill in order to prevent Nazis is enormous, probably in the thousands. It's not one easily removable Nexus point