Why are Grit and Darkside two separate abilities?

[Ditto]

None of this is unique to Drk. When a tank establishes enough of a lead in threat, they swap to their DPS stance if they can take the hits and hold threat, and prioritize damage.

Paladin has Fight or Flight.

Warrior has Maim.

Dark Knight has Darkside. It is our version of maim basically, only it is capable of having 100% uptime so long as we can fuel it, where maim runs on a static countdown, and no matter what, isn't going to apply to the first combo ability, nor Maim itself unless it is already up. Grit is ONLY ignored by bad tanks who think they're too good for a tank stance and like to put their healers and high DPS through hell, and those who know they can drop grit without putting their healer through hell. Warriors drop Defiance just as much for Deliverence, and Paladins with Sword Oath.