That’s Stars Arisen (Stars Arisen Developer Diary) btw 
Could lead to a cool parallel with England where there’s a culture based around training mages from very young like they did with archers, guns being the crossbows in this comparison. At least, this works if mages aren’t just stupidly powerful as they are in some fantasy so guns still have a use with a sheet number advantage. Not really worth fielding and supplying an army with food and equipment if a mage can wipe them out solo (at least for battles; occupying areas is still useful and likely not feasible with one person).