Those two, in tandem, are the most powerful combination of an two schools of magic or skills in the game.
Even sneaking everywhere you will level it quite slowly without using sneak attacks to advance the skill.
As long as you have one focused damage skill and a defensive skill or strategy, you will be viable in the game. Everything else you do is of sheer personal choice.
Even without being very stealthy early game, you will be a dominate force if you implement Conjuration and Illusion. This will hold true for any level of difficulty. Even Legendary. You will literally only be leery of being hit from those swinging axe hallways.