Also, many of them were too busy doing repetitive tasks and didn't have time to innovate. Technology freed us from many of the repetitive tasks that were required for survival, so we have more available brain time. Also, improved communication helps us avoid wasting time discovering the same thing over and over.

Medieval peasants had the same brain as we have, but without proper education, limited comfort and material means, days spent working the land, and slow and limited communication, no wonder much findings came of them. And because they didn't have the tools we have today, a lot of peasants were needed to keep the general population fed. Only the higher classes had the means to conduct proper research.

Today, at least in developed countries, it is like all of us, including farmers are "high class". We all have access to knowledge, instant worldwide communication, and some level of comfort. Repetitive, draining jobs are still a thing, but on a global population level, we need less of them for survival. Not everyone is a genius, but we have a much greater pool of available geniuses, and their abilities are better exploited.

Counterpoint, look around all all of the dumb people currently alive. We are standing on the shoulders of giants, true, but that giant is standing on a brobdingnagian mountain of stupid people.