I strongly suspect that many epic high fantasies were cribbed from an author's D&D session where s/he gave themselves God Mode Mary Sue
And while we're on the subject of Disney, a little part of me kind of wants to see their cartoon adaptation of The Diary of Anne Frank
. The same part which makes me want to also see them do Animal Farm and Lord of the Flies.
WARNING: Those links go to TV Tropes. I am not responsible for your loss of time or brain cells should you choose to click.
(ETA: The OP may find the "Literature" sections of the Villain Protagonist and The Bad Guy Wins pages to be Relevant To Their Interests. Lots of crime/horror/historical but also some fantasies described in somewhat spoilery detail.)
As for good fantasy novels with bloodily-pragmatic assassins/battle scarred veterans in the protagonist role, I recommend Mickey Zucker Reichert's The Legend of Nightfall
and the original Renshai Trilogy
(sequels not as good, feel free to skip).
The first has the assassin reluctantly roped in via magical geas to help out a naively would-be heroic prince on a quest. He's not happy about it and will cheerfully go to underhanded means to make sure everything works out, but the thing is he has to obey any order the prince gives him on pain of losing his soul, and the prince is kind of a starry-eyed parfait and gentyll knyght
twit prone to giving overly-chivalrous and honourable direct instructions, so the assassin has to sneakily work around that when he'd rather be doing some serious stabbing instead (preferably to said prince). It's a fun read.
The Renshai trilogy is set in an unusual world where the Norse gods are kind of real and the human part of the world has been divided into four alignments of Lawful Good, Chaotic Evil, and two Neutrals, and whose inhabitants are generally expected to abide by said alignments. The protagonists of this one generally belong to a Northern tribe which is considered by the neighbours to be secretly evil because of their combat-obsessed pragmatic approach to warfare, which lacks sufficient "honour" and thus tends to lead to occasional attempted genocides of said tribe (there's a decent chunk in the books about why Lawful Good can be neither and Chaotic Evil of occasional benefit).
Apparently a big chunk of what happens is part of a plot masterminded by some of the Norse gods to try and stave off the inevitable Ragnarock and there's plenty of maneuvering and backstabbing which Our Hero is none-too-pleased about being pushed towards a Glorious Destiny of. Again, lots of fun if you like seeing people around him being shocked at his seemingly-callous-to-them tactics.