I can help you for Britain, though I suspect many of the core dynamics were the same in basicaly any bread-baking society.

At an empirical level, this question would be difficult to answer because to my knowledge census data is pretty slim for the medieval period. Later on, we have industrial directories that allow us to count the number of businesses in places (with some caveats), but again I don't believe those exist in the medieval period.

But, we can still work things out to some extent by working backwards. Four bakers for a 2500-person city is not TOTALLY out of the realm of possibility; I'll have to check for you tonight but Petersen's Bread and the British Economy provides figures for the number of bakers per capita in several 18th-19th century cities, and the technology by then--for baking--was not really that different than what medieval bakers would have used. Petersen's figures vary widely, but if memory serves (you'll have to wait until later tonight), it was something like 500 people per baker. I don't recall if that's per baking establishment, or per individual doing baking labor. I can tell you though, that baking well into the 19th century remained a small-scale trade. Typical urban shops did fewer than ten sacks per week (more on sacks below), and were generally a master, a journeyman or apprentice, and then a boy to haul water and firewood.

Now, how much bread are the actually baking? The Assize of Bread was a medieval law that tied the price of a loaf of bread to the price of grain, with certain allowances for the bakers' labor, cost, and profit. It was instituted first in the 12th or 13th century, and was not fully repealed across Britain until 1836 (though by that time it was essentially out of date). In order to calculate prices, however, it relied on a baseline number of loaves that could be produced per unit of flour. The standard sack of flour in Britain in the early modern period was 280 lbs. The baseline number of loaves that the Assize expected bakers to bake was 80 "quartern," or four-pound loaves. You could also baked 20 "peck," or 16-lb loaves. Most bakers managed a little more than that, and there were some mechanisms in place to vary the size of the loaf somewhat depending on the price of the wheat. However, as a rule, one could expect a baking establishment to do one sack of 280 lbs of flour per day, and each sack to work out to about 80 loaves. So, you're talking about at least 320 lbs of bread per day. Given that, when we have reliable figures in the 18th century, the average working adult ate slightly under a pound of bread per day (yup), then that's theoretically enough bread for, say, 350 to 400 individuals. And that's not terribly far off from the number of bakers per person that Petersen identified in the 18th and 19th centuries. Mix in the fact that some people are going to bake their own, particularly the medieval period, children will obviously eat less, and foods other than bread likely played a bigger role in medieval diets than in 18th-19th century diets, and one baking establishment per 500 people is pretty reasonable. And, that medieval town generator thing doesn't seem too far off.

See:

Christian Petersen, Bread and the British Economy (1994? Looks like Taylor & Francis reissued it in 2017?)

John Bohstedt, The Politics of Provisions: Food Riots, Moral Economy, and Market Transitions, 1550-1850 (2010)

Edward Thompson, "The Moral Economy of the English Crowd in the Eighteenth Century," Past and Present 1971

James Davis, "Baking for the Common Good: A Reassessment of the Assize of Bread in Medieval England," Economic History review 2004

Alan Ross, "The Assize of Bread," Economic History Review 1956

There's a range of other sources floating around out there, on related topics but none that I know that directly address your question