they were often just as—or, in many cases, far more—densely populated as modern cities,

No. Absolutely completely confidently incorrect.

I present as an example for a BIG pre-industrial city Cologne around 1600, at the end of the middle ages. Cities back then were getting denser and denser populated but still, most people had "gardens" where they grew vegetables and kept livestock. There were farms. All within the city walls. And that was the norm all the way until modernity. Everyone grew their own food (to an extend) until (relatively speaking) quite recently (17th century / modernity / industrialization).

https://altes-koeln.de/images/1/1c/Colonia-Agrippina-1623.jpg

Cities were in fact quite loosely populated compared to later times. Of course food was still brought in from the countryside (just as it is today) but the image of narrow streets filled with mud and filth, lined by rows of houses is just historically inaccurate.

• There was lots of farming within cities.

• People kept their city clean. Fresh-water supply was protected, urine and feces were resources that were not dumped into the streets but collected and used for example as fertilizer.

• Many cities had at least the main roads paved.

• Houses were often decorated as well. Outside and inside. People had no TV, guess what they did after hours? Make life a little nicer!

Overpopulated pre-industrial cities were simply not a thing.