The accuracy of Damnation is just bad. It's bad on Thaum with 50 DEX and with 15 DEX, it's bad with 20 or 60 PIE. It's bad on every other disciple I use it on. It's a good ability, but I think they gimped the accuracy too harshly because it returns some MP. I use it whenever I can, but I never rely on it.
After mucking my stats around for awhile and playing for a couple hours with both stat setups I can honestly say that I didn't see a difference.
That's because stats just have such a small effect at lower levels. I personally leveled up CON and THM with like 80 VIT and 45 MND, and everything else in the teens. I was just as effective damage wise as a traditionally built mage, but with a lot more survivability and bigger MP pool.
I find gear to be a lot more important than base stats. I bought a new Scepter which upped my M.Acc a good amount, along with 4 Bone Rings for even more M.Acc, and I noticed my Damnation's landing more often and for more damage, which makes sense because my new weapon increases my M.Atk as well.