Well it's not really a tough stance on horror because I don't think that the "negative" connotations of GrimDark neccesarily means that such games are unplayable or not fun. I don't really have a firm definition but taking a cue from other kinds of media I would say that wallowing in a nihilistic pose, engaging in lurid subject matter or just generally presenting a setting where the participation of the PCs generally does little to affect the overall nature of the setting. Understand now, that my definition has really got nothing to do with this thread but since you asked.....
Regards,
David R
Hey, every opinion matters, and the OP was just a not - so -subtle stab at Warhammer, so it's just as much on the topic as any other post, because there's no definite definition (tautology, I know, but bear with me) of "grimdark".
I'd personally say that what you described fits more for a setting that's tragedy then grimdark, as grimdark has a connotation of farce and hyperboles being a very strong element of it.
In fact, I'd say that someone should make RPG based on an idea of a Greek Tragedy and Nemesis.
Nemesis as in the concept of fate being impossible to defeat, not Nemesis the RPG
.