Issue with TBN

[Reynhart]

You get a shield

Something that other tanks have without any risk at all, and completely free.

and you get a chance to use the damage move.

A move that you could have used instead of TBN.

DPS wise, TBN is at best neutral. There is no "reward" at all.

However, if we want something less straightforward than a Crit buff, we could have Dark Arts only last for a set duration (Like 10s) and, while Dark Arts is active, you gain a slight speed buff. Of course, Dark Arts will wear off if you use Edge/Flood so you'd have to make sure you don't need to refresh Darkside during the duration of Dark Arts.