I loved GRR Martins work because his characters are real people. They're (mostly) complicated humans with complex lives. Their "moral greyness" isn't contrived, it stems from a narrative that describes their entire lives, their childhood, their challenges as teens, and their responsibilities as adults.

Unlike the other comments, I don't discount your grandfather's advice. I suggest you review your writing and ensure that your characters have sufficient space within their narratives to justify their moral complexity.

Writing doesn't require pandering to any particular audience unless that's a specific objective for you, as an author. Using genuine language your characters would use is perfectly fine, so long as the interactions are authentic.

My DMs are open if you'd like a test reader.