Tbn
Cost: 3kmp
Reward 1: 500 potency (DA)
Reward 2: 25% hp shield.

Dark arts:
Cost: 3k mp
Reward 1: 500 pot
Reward 2: nothing

All this talk about 'where's the reward'. Are you blind? Dark arts does 1 thing. Tbn does the same thing as DA but adds an entire other funtion at zero additional cost. If a candy bar costs a dollar, but the store next door sells a drink+candy bar for 1 dollar, which one has more value?

If you want tbn to INCREASE damage, then go ahead and give shelltron a shield swipe proc and raw intuition equivalent counter attack. Because thats what you are asking for.