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You've certainly ramped up the grimdark a bit! That said, I can think of a number of successful fantasy series which aren't a million miles away from yours. John Wyndham's The Crysalids is almost...
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You've certainly ramped up the grimdark a bit! That said, I can think of a number of successful fantasy series which aren't a million miles away from yours. John Wyndham's _The Crysalids_ is almost the scenario you describe, except that mutants are executed (although torture for information is a thing). The _X-Men_ series is less horror-based but socially is very similar to your setup, including experimentation and vivisection. And _The Handmaid's Tale_ book and TV series presents a fairly similar society if you consider "female" to be "the other". On the grimdark front, you need to demonstrate a need for that grimdark to exist. If you can, then fine. But your character also needs to react appropriately to it, and not be miraculously unscathed. Sheri Tepper's _Beauty_ is not a fluffy fantasy, but every step along the way is necessary. Stephen Donaldson's _Thomas Covenant_ and _Gap Cycle_ are probably even more intense than your setting. You might also consider the 2000s _Battlestar Galactica_ reboot where humans take revenge for their losses by torturing captured Cylon hybrids, showing us Admiral Adama's moral core in comparison to Admiral Cain. And of course there's _Game of Thrones_. So I don't think you need to be afraid of your setup being too depressing. What you need to do is have something to say about it. It may be hard to find something original to say which hasn't already been done by some of the examples above, but that's where your writing ability comes in. :)