It's pretty obvious from recent well recorded history that leaders with the necessary skills, motivation and right time/place fitment to actually do world changing things are incredibly rare and when those kind of people do pop up we get world changing events that would have never otherwise happened or if they did would have happened with vastly different details and consequences.

The great man way of describing history leaves a lot to be desired but the "somebody else would have done it" crap is even worse. Remove key figures from history and then try to judge what would have happened had someone else filled their shoes and it becomes painfully obvious. Imagine 9/11 happened +/-20yr. How would the second half of the 1900s played out had Chaing Kai-shek gotten control of mainland china? Would we have gotten the napoleonic wars if Louis XVI kept the throne another 10yr? What would european history look like if church had waited another 200yr before cooking up the idea of the crusades? Imagine if the US hadn't elected an abolitionist sympathizer in 1860 but instead waited until 1872? How would recent European history look without Stalin? Etc. etc. Key details regarding when and the order in which events happen have a huge impact on history and the whims of individuals (like Alexander) massively influence these details.

I'm not here to defend the great man theory of history. I'm here to put the "it mostly would have happened about the same" theory of history in the dumpster where it belongs.