TBN Should have a 30s cooldown and merged with Oblation for a 7s shield and 10s 10% reduction and still give Dark Arts on a broken shield, but have its MP cost removed and have Dark Arts reworked to empower the DRK defensive tools instead. Each time a defensive tool is used with a charge of DA available, it automatically enhances it. You can lock the healing behind a broken TBN and implement other effects behind different defensive tools, the only catch is TBN has to break and you don't have a choice in when DA takes effect; it is always your next defensive.

Bring back Dark Passanger, put it on GCD and make it consume 15s of Darkside time. Put Abyssal Drain back on GCD and make it also consume 15s of Darkside. Obviously, neither ability can be used unless under the effects of Darkside.

That'll probably fix most issues, including the underperforming TBN. One I wish people would stop saying is so great when it really is the worst of the other tanks options. I'm also just BEGGING for interaction with our Darkside gauge. Why do we even have it?