When I do allow magic, only allow the subtle communications, empathy, and mind spells (GURPS). Basically spells that do not affect economics, politics, and technology so adversely and can be conveniently removed from the narrative.
Along with magic, I apply the harsh realities and challenges of education and communication of ideas. Knowledge is very fragile and a lot of it failed to survive time, despite their utility. The axial age of human history saw the flourishing of so many ideas which many were destroyed when an ideology comes to power. Ideas that could have been refined and tweaked to fast forwarded humanity into a brighter age.
Spells with its complexity and inconsistencies is similar to economics, psychology and medicine which are very hard to advance because of their multitudes of unobservable factors. If one were to limit magic to mediums of communication to that of the Ancient World, spells as complicated as
Modern Day Magic: Lie Detection is modern day magic. If deception expert were to go back in time he would be called a wizard. Economics, Negotiation, Sociology, Psychology, Math, Engineering are all skills that can mastered by an individual inclusive of any aids and applied with devastating consequences when brought to times of the past.
I frequently wonder what I could contribute to the Filipinos of the 19th century so that we wouldn't end up exploiting each other for generations. If I could offer my services to Antonio Luna and Andres Bonifacio when they needed good people around them.