Grimdark is good when hogs can oink and happily eat from the slop trough.

Grimdark goes too far if the hogs actually feel uncomfortable while eating it.

I think this applied to most of the exhausting and fortunately expired zombie fad that lasted roughly two decades: hogs liked it when they could fantasize about being tough and rugged and independent and slaughter their "zombified" neighbors and anyone that got in their way while establishing their own private Republics of Dave. The real horror there, to me, was the power fantasy itself and the fandom that wrote exhaustively about what they would do during a "zombie apocalypse," usually with a giddy, excited tone.

I now doubt that many loud and dedicated consumers of the zombie fad were actually into being "horrified" as much as getting a rush from the gory spectacles, tacticool peacocking, and the libertarian spank bank potential of such collapse scenarios. "spez" of Reddit comes to mind there.

EDIT: I admit I am now intrigued by the scenario concepts mentioned in the OP. It seems like it's going somewhere with it besides "hey look more gratuitous sexual violence which is totally not condoned by the narrative or intended to be entertaining for the audience, for real, while getting full frontal repetitive focus" and/or "look at these badass dudes getting shit done and making the hard decisions by doing atrocities."

EDIT of EDIT: I can totally see an Amnesia/Machine for Pigs style treatment of the OP setting.