I am writing this with the caveat, "I am not a historian, but..." I am working on a multidisciplinary Ph.D. that focuses on leadership, and I know a bit about the history of "Great Man Theory". While I can't definitively say "Great Man Theory" (GMT) is not some one person's world view, who can really rule something like that out given the wide variety of opinions, I can tell you about the origins of the theory, how it has progressed over time, and where it is today from a leadership studies perspective. I am attempting this answer to give you some clarity as to what modern scholarship believes about leadership, if not to give you precisely what you're seeking.

For our purposes, I will define GMT as the idea that an individual imbued with special characteristics must be produced for leadership to occur (Northouse, 2022). In a historical context, this would mean that, for there to be a leader, there must be a person created through providence, the will of a deity(s), fate, or genetics if you're a person of more modern sensibilities (Bass & Bass, 2008). GMT would posit that, if your society had not produced such a person, then you were out of luck. Should another society come along with such a leader and decide your land looked good for the taking, then that was that, and no amount of pressure or change would cause a leader to emerge and protect your society if that person did not already have what it took to lead (Bass & Bass, 2008).

GMT theory has always, sort of been around. We see examples of society producing legends and myths of great leaders over time to use as an exemplar for others to follow, aspire to, or as a tool by which people could recognize the emergence of valid leadership. Examples include but are not limited to Prometheus, Moses, or figures from the Upanishads or the Iliad (Bass & Bass, 2008). Writers and philosophers extensively wrote about leadership and what it meant to be a leader. They hoped to analyze leaders to determine what it was that made them so special, assuming that leaders had some otherness about them. One particular notable attempt was produced by Plutarch in his work Parallel Lives, where he compared Greek and Roman leaders to argue that a shared set of traits lay within both sets of leaders across societies and across time, producing similarly effective results (Bass & Bass, 2008).

At the beginning of the 20th century, a guy named Ralph Stodgill took something like 130 papers completed up to 1948, compiled all the stuff, and realized that relying wholly on the features of a leader's personality, like intelligence, gregariousness, etc., didn't work without accounting for what was happening around the leader at the time the leadership emerged. This was further reaffirmed in another publication, again by Stodgill, in the 1970s that took even more studies, and showed, yet again, there was a bit more at play here.

At this point, scholarship started branching out into other ideas and looking at things like leadership behaviors, the settings in which leadership occurs, skills and competencies that contribute to leadership, etc. The research focus drifted away from GMT and more into studying leadership within the framework of a complex system. John Lewis Gaddis would be proud.

Here's where things get tricky, research on personality and genetics continued and matured alongside scholarship into the traits of leaders, and as we dip into the 80s and 90s, we start to see a return of inquiry into leadership traits, the underpinnings of GMT (Northouse, 2022). This happened because new tools and new techniques made it easier for scholars to uncover patterns between traits and leadership. Genetics and genome mapping allowed tight correlations to be made with leaders and their characteristics.

The difference between GMT and the theories being developed at this point in the history of leadership scholarship is that scholars are now accounting for complexity. Sure, we know that intelligent people tend to lead well (to a point, leaders who are more than a standard deviation in IQ higher than the groups mean perform poorly (Bass & Bass, 2008)), but that's not the only reason they lead well. They lead well because they have experience, knowledge, skills, and technical competence, the situation is right for all those things to come together, and also don't underestimate the importance of luck. Integrity and values and how reflective a leader is of the group's values play a role in leadership effectiveness and selection. Also, how society sees itself and its leaders are taken into account. These variables are all now considered (Bass & Bass, 2008).

Circling back, basically, people are complex, and systems are complex, and GMT is too reductionist to adequately explain why leaders are chosen and why they are successful (Bass & Bass, 2008). Much of the early scholarship done on leadership, and the scholarship that supported GMT, was biased by the systemic exclusion of minorities and women from leadership roles. Weird things show up in early research, such as how manly someone is being used as a benchmark for how well they lead, and many ideas that we would consider misogynistic or authoritarian today were considered good theory. Some works focused exclusively on children or men in the military, further eroding the value of generalizing the findings due to poor sampling.

As it relates to history, I will lean on one of my favorite authors, John Lewis Gaddis (2002), and his book, The Landscape of History. Gaddis writes that the study of history is too complicated to take a reductionist perspective, and to try and narrow down one set of traits in one or even several leaders to adequately explain the EVERYTHING happening at any given point in history is impossible. Gaddis believes that the social sciences are more easily explained by chaos theory than anything else, a sort of mathematical chaos where random organization happens and then disappears again over and over again over time. Given how complex the universe is and how complex life is, there's no possible way we can adequately explain events as large as the second world war or as small as the Potsdam conference without considering more than just the men at the table. Gaddis believes that good history doesn't strip away the context to find the independent variable, but crafts a narrative accounting for all of the color of the human experience. To strip it out and ascribe it to a single man denies the world its place in history.

References

Bass, B. M. (2008). The Bass Handbook of Leadership: Theory, Research, and Managerial Applications (4th ed.). New York, NY: Free Press.

Gaddis, J. Lewis. (2002). The landscape of history: how historians map the past. Oxford: Oxford University Press.

Northouse, P. G. (2022). Leadership: Theory and practice (9th ed.). SAGE.

There is always more to say, but this older thread, with u/commiespaceinvader, which looks at Hitler as an example of a supposed "great man", and examines the main flaws of such a presentation, is insightful and still worth reading.