“Certainly not every book or series should take place in an egalitarian society…”
Of course, not. The structure of the society is only a backdrop for one’s story, and if the author wants to, he or she can develop a powerful character of any gender, even if the person is hereditary born into a cast of sex-slaves. Only the story matter, and only the story dictates, whether your protagonists and antagonists are men, women, whites, blacks, greens, purples, gays, straights, orcs or dwarves.
It is indeed, unrealistic to have unequal ratio of sexes in the secondary world, which is modeled after our own (unless this is a pivotal point of the plot), but it is also unrealistic to slap a gender upon the character only for the sake of political correctness — it will read forced and unnatural.
In a sword’n’shield world the expected role of a woman was mainly to make more men: noble scions to rule, commoners — to fight and die for them. It is expected by the reader, even superficially familiar with our own history.
That is why it is much easier to toss a male character a sword and kick him into a noble quest to fulfill some lunatic prophecy, than write a convincing and strong female character, doing all the cool things.
And this is why it is also so, so unoriginal…