Equestria is dead, the world got nuked with necromantic radioactive hellfire, and in an underground bunker, society has fallen apart and declined into a caste society based on species. Are the inhabitants of this vault truly even still ponies?

nothing is too dark for dark that's why its dark

It's not too dark. Then again, my favorite fictional city is Gotham, and I also am part of the FNaF fandom, so WTF do I know?

I do agree with the other person there's nothing that is too dark but there is different levels basically what did you intend for your story to be dark or grim dark cuz if you wanted to make it extremely dark that's fine you just got to think of what level you want it to be and what level can be a compelling story that you can write

The bottom line for any Fallout fanfic is the premise of your story and everything that comes with it (Rapist raiders, Lunatic atomic cultists, etc) so no, it's perfectly ok. It does belong here though