High Dex does not translates to better defenses.
Parry is equality affected by STR and Dex.
High dex translates to better AC which translates to mobs miss due to AC and less damage.
Of course Illithiad can hold a shield and a Stave/Wand, increasing their AC and saves by a lot.
Cursed staff is nice, until the moment they start dualing Axes you know zero about. That's when you wish you had the Racial Parry of the Squids. Good thing that if you have pets, you will mostly be facing defensive weapons like Staff,Polearm , spears+dagger.
Don't see how you get a Powerword due to sneak.
From my experience you mostly GRASP when they are lagged by pets and not aiming at you. Then you Flee and Powerword. They can't block your power-word, cause they are already engaged, or lagged, or running away.
Unless you are meaning that you are trying powerword/Sleep with no pets. Which in my opinion is suicide. Necros unfortunately cannot do it without pets, due to the harassment/disturbance they represent on your opponent.
Also, Humans can apply for Lich.