Same issue here, on master difficulty, and I too found Illusion to be invaluable early on. It's not the solution to every problem though, like in dungeons where it's practically useless until much later in the game, but otherwise it helps a lot. Fury is especially fun, but it works only up to level 6, however Calm is amazing. Before, I would get ambushed by a big cat, witness my merc die, and then be forced to run away with no magica left from trying to kill it and of course die soon after, but now a simple calm will do and I can move on. I think only 4 perks are needed for Calm to work most of the time too, which is nice. It almost feels like cheating sometimes, because no one will cast calm on me.