I recently created a 1024x1024 test map, in the year 1785, with all default settings except that "Large Cities" was set to one. The largest city on the map was very large indeed, at nearly 170,000 inhabitants:
Is this a bug, or are "large cities" meant to be this large now?
I do not think that this is a bug, but I cannot recall what was intended for the size of large cities; I think that it is randomised to an extent. You can always set large cities to zero, and you will get a nice, realistic zipf distribution of town sizes.