Thats why illusion is there. Illusion is powerful because you turn master-level enemies against eachother, then you just use your not-so-powerful destruction to finish them off. You're looking at it too black and white.
For example, fury and whatnot are extremely powerful, and are in place of the power 2hs give.
I don't exactly agree with it, but i see what they were trying to do.
Thats nice.......but that like saying this of a thief/assassin character.
Oh your dagger isn't doing enough damage? You have to use pickpocket first and weaken them first. Could imagine how much assassins would svck is daggers didn't do enough damage to mostly kill most enemies. And you then had to use the majolrity of the thief skills in order to kill something.....it would svck.
It a different way of playing....in all the other playstyles you can focus on a particular skill, mages cant else they aren't powerful enough. Meaning the ever mage that is actually playable end up being a mix of destructor, illusion/alteration and conjuration.