I have played as a corrupted sorceress from day 1. Not full corruption, but 37.5% permanent corruption.
Specifically, here is my build:
To say that it is not viable or unplayable is simply not true.
With 15 points worth of Grotesque Excrescence, I regenerate six times faster than Fierce Vitality. Twisted Flesh causes 7.5% of attacks against me to do no damage. Petrified is, in my opinion, one of the best perks in the new attribute system.
However… I absolutely cannot fight toe to toe with someone who is not corrupted unless they are significantly less skilled. Sorcerers are supposed to be weak, but I will agree that this weakness is a bit too much.
Additionally, while a sorcerer should not be capable of winning in a fair hand to hand melee, they should be capable of winning an unfair magic versus sword fight.
Our current magic selection is too limited. I will point out the original intentions for Sorcery laid out by Joel Bylos seven years ago:
Necromancy: Implemented, but not to its full potential.
Demon summoning: Implemented, but very underwhelming.
Transformations: Unimplemented.
Illusions: Implemented and one of the peaks of sorcery.
Transmutation: Unimplemented.
Ripping out a man’s heart: Unimplemented, and this is exactly the type of sorcery we are missing.