Short answer is, the Ancient Greeks and Romans were not more knowledgable or even necessarily wealthier than Europe during the Middle Ages. And if there were any shortcomings, it was due to environmental factors rather then a lack of knowledge. Proof can be seen by the large castles, churches, and cathedrals that were made during the “dark” ages. Those were not made by dumb people.

It’s a common misconception that after the fall of the Western Roman Empire that Europe entered into the “Dark ages”. Medieval Europe still knew the stars, calendars, knew about plumbing, how to craft steel and plate armor, even better than the romans did.

After Rome collapsed, free trade become very difficult without a central system of government and commerce protection, trade routes became susceptible to raiders. The silk road was also severely cut off from Europe after the Rise of Islam that dominated the east. So in a sense yes they were “poorer” than they were before, but if you would pit a Medieval soldier versus a Roman Legionnaire, the Medieval soldier would still win. Even the lives if the average person would have been largely the same. It wasn’t until the rennescance and the invention of gunpowder did peoples lives on a large scale begin to improve.

In Medieval times much of society had to take shelter behind heavily fortified towns and walls, where mass plumbing would be hard implement even though they had the technology. Thus making people susceptible to disease.

There was of course the Black Plague that struck Europe, which decimated its working class. If you are getting the gist of what i’m saying, the Medieval people were no more stupid than in times before necessarily. The average person just had a far wider array of problems they had to deal with.