Cora I actually agree with Xiao on this. Having MPs and being able to cast a defensive (as I called it when I wrote it the first time) Shield, is the only real defense a gnome or dwarf has to magic. And it would make Elves sell MPs even more. Also, every race is supposed to be able to cast, albeit Dwarves and Gnomes get horrific downsides to that. ie horrible upkeeps, reduced chance of success. Elf does get spell bonus, and I love that for them.
I do agree that MPs should never cast offensive spells though, but defensive is great. Maybe make it so that you have to tech into the defensive spells though to use MPs that way. Then it will be a small commitment. For someone like me who is a gnome, it's been obvious to avoid those techs in the past, but now that I can cast GB on myself with MPs, it's worth getting that tech tree.