I appreciate the question, Vauclair.
The problem is, you’re perceiving the past through the lens of modern history-making. From the 1700s until the recent past, history generally but pre-modern and non-European especially was written with a very specific set of cultural and gender assumptions. Over the past few decades (what someone in this thread derisively called “Revisionist History”), historians and archaeologists have tried to stop working from these assumptions, and look at the actual evidence.
All too frequently, when academics go back and look at that evidence while trying to set aside these assumptions, they discover that history is not as it was taught to us for three hundred years. (There’s a great recent example regarding Vikings, where bone-studies upended the assumption that people buried with weapons were men; turns out, women were buried with weapons as well. http://onlinelibrary.wiley.com/doi/10.1111/j.1468-0254.2011.00323.x/abstract)
When you and Rogar make claims about a “traditional society,” the problem is that we don’t have much evidence for what life was like–especially for poor, rural, illiterate villagers. When you say “traditional society,” you’re talking about what the religious figures (the educated people of the time) of the 18th Century were projecting back as being eternal and unchanging, not about how the past actually was.
Thus, claims by you about what medieval life was actually like, without rigorous academic evidence, are specious and likely bigoted, because they arise from the political historicity of the modern era.
Now, I’m not saying that I personally know how nonbinary people were treated in medieval Russia. What I am saying is, claims that they didn’t exist or that this is an inaccurate portrayal of them is incorrect, because no one knows the answer. Therefore, your rejection of the inclusion of nonbinary people in this fictional past is a political stance, not a historical one. Conversely, this also means that the inclusion of the nonbinary sibling is a political stance that this story takes; but I know that it’s a political stance, and I’m ok with that.
This is why I asked you to stop saying bigoted things: by trying to frame your argument as based in historical fact, you’re asserting that your argument isn’t political. But there are no historical facts on which to base your claim, only modern political opinions. As long as your assertion is based on a modern political opinion that is rejecting inclusivity, your statements are either ignorant or bigoted.
Here are a number of links about politics, historicity, and fiction: