Grimdark is often called hopeless, but in doing so people miss that it isn't apathetic - it is (for me) characterised by defiance in the absence of hope.
Grimdark is often called nihilistic, but this misses the idea that you can accept a nihilistic truth and still choose to die for a principle you know is an emotional construct.
A grimdark "hero" has a tendency to go all in - to burn their bridges even when they don't need the warmth. They are, in their way, an allegory for hope, in so much as having been shown there's no meaning in the world, they still cling to some elements of it. And in those choices they are revealed.
The way it's painted by the disapproving you would think that grimdark fiction was the literature of surrender to the inevitable. When in truth it is the story of the battle against it - sharpened by the knowledge that there's no ultimate victory to be had.