TBN is the only defensive ability (belonging to tanks) in the game that is in direct opposition to offensive skills. The TBN shield may be awesome, but losing 500 potency when it doesn't pop is just garbage. Easiest way to fix TBN is as follows:

Remove the mana cost on TBN, remove Dark Arts entirely, and increase the TBN CD to 25 seconds. This will eliminate the issues with TBN being a damage loss when the shield does not break, while also bringing it in line with other short CD tank abilities (Shelltron, Raw Intuition, and Heart of Stone)

Also, give Dark Mind a 10% physical damage reduction in addition to the 20% magical. This one is obvious........