Oddly enough, the question of historical realism seems to crop up with a degree of regularity in the fantasy genre. I’m not entirely certain why (as I’ll explain below), but suspect it has to do with the Eurocentric medieval roots of the genre. That said, the entire genre has a sliding scale from utterly non-realistic to hyper-realistic that cover the classics (Tolkien, Moorcock, Leiber, Howard, Moore, Bradley) to more modern names (G.R.R. Martin, Rothfuss, Jemisin). But, even the medieval roots—ex. Chrétien’s Yvain and Lancelot, Gawain & the Green Knight, Beroul’s Tristan, William of Palerne, Marie de France’s “Yonec” and “Bisclavret”—weren’t exactly realistic beyond a certain point.
More often than not, it seems that claims or cries of “historical accuracy” are used to justify rampant sexism or racism in a work. This appears to be more of a fan thing than an author thing in most cases, though there are exceptions (as shown by some of the so-called Sad/Rabid Puppies). But, most of these appeals to “historical accuracy” are based on outdated or outright false history.
All said, I’m not entirely certain that “historical accuracy” has a place in the fantasy genre as a whole, at least in most sub-genres. It is certainly important in historical fantasy (although differences in history can be explained away as the influence of magic), some urban fantasy, and, of course, alternate histories. But, in epic fantasy, sword & sorcery, and other secondary world fantasies . . . no, Earth’s history has no bearing on the secondary world. “Historical accuracy” in the case of a secondary world fantasy should never refer to Earth’s history (even if the world is based, however loosely, on Earth), but rather to the secondary world’s history, much of which the reader does not know (exception: Middle-Earth, thanks to the posthumously published Silmarillion, but even that is not a complete history).
Although speaking of the RPG industry in general and D&D in particular, I think Forgotten Realms guru Ed Greenwood put this best for the entire fantasy genre: “But D&D has half-orc, and half-dragons, and half-elves, and has magic items that specifically change gender, right there in the rules. Surely if you can handle the basic notion of cross-SPECIES sex, having a full variety of gender roles should be something that doesn’t blow your mind” (Facebook post, 5 April 2016).