"Doesn't cause breakthroughs out of nothing"=/="isn't a relevant component". The geniuses of the world can all have differing opinions even if they're all equally intelligent, and slight errors can matter--and on top of even that, the less intelligent people aren't even necessarily going to be interested enough to take the time to solve all that. If you remove all the people who'll have the proper opinions, and replace them with less brilliant ones, then the improper opinions would just be listened to because no one would contest them.
If someone like Stalin came to power in post-WWI Germany, it would not have been the same as when Hitler controlled it. Stalin wouldn't have carried on the war in Russia the way Hitler did--and there were lots of different people in power in Russia in real life as well, although not in the highest position--all with different attitudes. So someone like Stalin (although probably a better speechmaker) coming to power there wouldn't be impossible. For one example of why that's not true.It's like with historical tyrants. Killing one wouldn't change anything - they are a product of their own society, even if one of them was gone or removed from power the society would find a different one soon enough.
(As for why I say that someone like Stalin wouldn't...well...Stalin couldn't imagine that Hitler would.