You seem to subscribe to the "great man" theory of history, while the people that disagree with you subscribe to a "human dynamics" theory of history (think Hari Sheldon's psychohistory in the Foundation books). You can point at some "great man" in history and say "if it wasn't for this person's actions history would have been different", but over long enough timelines I believe some things are inevitable, given the wider context in a point in time. If Columbus hadn't convinced the Spanish crown to seek new trade routes through the West, some other individual would have enticed another colonialist European power to so, with similar results for native Americans over the following century, for example.

> You must admit that the genesis of a great man depends on the long series of complex influences which has produced the race in which he appears, and the social state into which that race has slowly grown. ... Before he can remake his society, his society must make him.

— Herbert Spencer, The Study of Sociology