New Fantasy Setting Seeds.

[Rolando]

Also slavery means lack of freedom, not necessarily lack of comforts.

Maybe slave mages can't go wherever they want but they are granted a good life and other slaves as servants and company; people in many countries in the modern world have a similar agreement with the companies they work for, they just get money enough to have a life and some comforts and they have to work "like slaves" or be dispossessed, they can change jobs of course, a slave can't, so these people are free to chose and move, even of starting something on their own, or just chose hunger and risk, but they are not slaves.