I'm pretty convinced that growing up and living in their era encouraged and different type of think that made them more wise than people these days. Most people these days are smarter than aristocrats back in the day, but the type of think is much more narrow.
The average revolution-era aristocrat was of average intelligence. Thomas Paine and Jefferson and Washington were not average.
The smartest people in any era, in any country, are smarter than the average person in any era or country.
Human intelligence has not changed at all in the past 300, 3000, or even 30,000 years. The average person in republican Rome was as intelligent as the average person today, and their geniuses were as intelligent as our geniuses. Intelligence is not your ability to regurgitate era-appropriate facts. Knowing that gravity exists doesn't make you Newton's intellectual equal.