Originally Posted by
Jinze
Magic in the Witcher world isn't actually hereditary unfortunately. In fact mages "breeding" so to say, especially together, has a higher risk of leading to medical issues. Vilgefortz was also an anomaly, the most powerful sorcerer known to man at that point. A lot about him is entirely unkown as he rejected his initial recruitment into Ban Ard (the male mage school) and went about on his own instead. Weaving magic and the staff he uses together in combat wouldn't allow for a Witcher type of combat in that sense, you wouldn't be a Witcher anymore, you'd just be a sorcerer.
I'm also not entirely sure whether the need for Witchers is as high as we'd like to think. While an all out conjunction right here right now at the time of the Witcher 3 would be disastrous, we already know that regular knights are becoming more capable in regards to monster hunting. The Flaming Rose even focus on it in large parts and in the books it's said that the biggest threat to humanity would really just be dragons (they're mostly extinct as far as we know), not regular monsters. Regular monsters are seen as a nuisance at best and while they require a bit of manpower we also have to take into account technological advancements. Monsters are already somewhat dealt with now, but once better weapons become available there will be even less need for Witchers.