I've encountered this problem before. Damn, how much money I spent to level up Wolfenstein in the campaign to get a super ability. It took me a very long time to get the Summoning magic, as it only has a 4% chance of appearing. But in principle, this is also an option: on a large map, you can level up however you like, and when you have plenty of money and a mentor, you can re-specialize the hero into a Super Archer, although it's not as easy as it sounds...