As far as geniuses go, many of the people we would think of as geniuses today have two things the people we are discussing here had not:

- They are able to stand on the shoulders of a far broader range of giants, thanks to writing; and

- They have access to far more tools of reasoning (arithmetic with Roman numerals is just the start!) that those in the past did not have.

So while there may well have been intellectual equals to the geniuses of today also back then, they would not have been able to perform the feats of geniuses today. Again, for lack of tooling, not wit.