That sounds like a good idea but my idea in my systems was for the sorcerer to more or less be like you described( With some major differences primarily they can be taught and must learn magic and it isn't a random personal gift) with also some being much like a necromancer except said sorcerer would mostly show up in person with maybe some slaves, mercenaries, and magic constructs/summons for backup and may only seek conquest of your fort as opposed to total extermination of life also the precise use of sorcery by the player is intended to only really occur in adventure mode.
In contrast hermetic magic was something thought up with the expressed intent of being something societies possibly player controlled would use to achieve desired affects but only if they can pay the costs and are willing to take the stigma that should be associated with it and sorcery(Being declared a sorcerous nation resulting Religious crusades and refusal of trade breaking of alliances and assorted agreements by certain civs and possibly abandonment by ones own civilization and the halting of most migrants with maybe rebellion by citizens of certain religious background if such activities where to become known to the world at large also possibly increased attacks by evil nations as you have no allies meaning no assistance by other civs and no starting wars with multiple civs).
Also i have some ideas for necromancers and deity granted abilities. My idea for necromancers are the ability to mark a person for a certain amount of time and if they die you get their soul and you can use this for special abilities like touch of death, cursing either with ill fortune or possibly death under certain conditions, making a husk, causing all the dead in a certain area to rise, and corrupting a biome.
Deity derived abilities should primarily be resistance to curses and evil influences with people who have a blessing being immune to curses or having their soul stolen or their body being raised as a undead or corruption of their lands and the high priests (not common clerics) should possibly be near impossible to be cursed or harmed by non physical effects of magic with no resistance to things like like thrown stones, fireballs, or having lava teleported in they should have no immunity but to things like mind control, touch of death, being directly effected by telekinesis, being turned to stone, or being teleported to a volcano they should be immune in every way and form with some abilities of their such as healing, resistance to harm and increased physical capabilities, the ability to inspire bravery in groups of people, and the ability to find the location of evil creatures and get visions of the plans of evil creatures.
What i am going for is that magic exists but it is mainly something that exists in remote places or hidden from the world and major incursions are countered by religious groups whose primary abilities is Resistance to many of the powers of magicians, Sorcerers, and necromancers of whom they will hunt relentlessly. Said groups should mainly consist of common people who join the cause in the event of a crusade or warriors and inquisitors belonging to religious orders who main purpose is to find various evil creatures who dwell in the country side and find evil creatures who hide in society and occasionally have crusades against Necromancers, Sorcerous civs, and large groups of monsters etc.