I had to assume 80%+ popularity of the Guild in Dran in order to recruit enough to keep running at listed level of economic output.
https://www.hcobb.com/tft/wizards_dran.html
If your guild is less popular than that then either the wizards just don't do as much for the general public as listed or you are using a vastly different magic system. The entire edifice rests on the underpaid labor of the Apprentices. Compare to grad students in the USA.