If you can deal void damage, most things can't really stop you. There are things that have so much resistance to magic and traditional damage, that you are screwed. Mage has a fundamental flaw where you don't know what type of magic a monster may be resistant to anymore without scan since everyone makes their own monsters. But in general, you only need to worry about the bosses. Without the proper proficiencies, you can't even use higher magic and being a mage is harder to do with limited mana.