This is more a historiography question than a history question, but it’s worth noting the “great man theory” hasn’t been debunked exactly. An extreme interpretation of the theory such as that by Thomas Carlyle, where the individual is more or less the singular force driving history is generally unpopular these days. However, there is a wide scope between singular individuals controlling destiny and great societal trends and forces creating a deterministic reality.

I think most historians today accept it’s a mix of both single individuals and larger forces. When you really dig into it it becomes extraordinarily hard to separate the two. Taking Caesar as an example, how much of history was determined by his will would be the first question, but there’s the additional layer of asking how much his individual will was influenced by, for example, Roman aristocratic society’s emphasis on great deeds.

There are theories which believe exactly what you suggested, eg historical determinism. Most notably in regards to the modern world, Marxist communism is based on historical determinism. Even here though, the determinism that is being talked about is only broad strokes, with plenty of room for individuals to shape it.

This is a quote from an article Marx wrote:

“Men make their own history, but they do not make it as they please; they do not make it under self-selected circumstances, but under circumstances existing already, given and transmitted from the past.”

I think this more or less sums up the majority of opinion around this issue, although the debate as to proportions is still ongoing and likely can’t be truthfully answered.

Edit: I’ve realised it might also be worth mentioning Karl Popper and his perspective on historical determinism / societal forces. He points out (correctly I believe, though there is still some debate) that societal forces, when broken down, are just the expression of many individual’s actions, and cannot be considered separate from these actions. Therefore, even if we accept “societal forces” over single individuals as the primary driver of history, what this means is simply that rather than a few great men dictating history, it’s the combined wills of many individuals. What this means is that the societal forces are not separate from individual agency exactly, and that history cannot be said to be deterministic even if led by trends and forces, as these trends and forces are themselves ultimately dependent on individuals. Its similar to the point I tried making previously about the difficulty in separating individuals from larger society.