It be fair it's vastly more historically accurate than say Skyrim or Baldur's Gate, and as any historian worth their salt will readily tell you original sources can only tell us so much about what was happening in any given time or place so even acedemic works on historical topics are faced with gaps as well as the native strugle with bias any human has when viwing anytthing.
To be sure it's a game and there are aspects in the game that 'short-cut' reality or make some things easier, the developers say as much in their own videos about the development process.
But there's still very much a sliding scale, historical fiction in books like Bernard Cornwell's Sharpe books are much more accurate than say George R.R. Martin's A Song of Ice and Fire books which in turn seem to draw more heavily from history than something like Dragonlance.
Unless we gain access to a device like the one written about in Michael Crichton's Timeline nothing we have game or book, for fun or education, will be completely historically accurate, but a mediveal setting without dragons, demons, and throwing lightning from ones finger tips will likely remain vastly more accurate than ones that include such things even if the PC gets to pick up new skills faster, or make money easier, than most people then or now tend to be able to.
I actually disagree with you that fantasy settings like the Elder Scrolls or Dungeon&Dragons are less historically accurate than ones that try to be realistic.
The simple fact of the matter is that settings that are pure fantasy have nothing to do with our history and therefore whether they bear any resemblance whatsoever to an historical time period in our world is entirely irrelevant. It's fiction, plain and simple.
On the other hand, a game (or book, or movie, or whatever) who does claim to at least partly represent part of our history (whether they're alternate history, historical fiction or an actual documentary) can be judged on its accuracy. Which is probably one of the reasons game developers don't use that kind of setting more often, since proper research takes time (and therefore money).
That's one perspective, and you are entitled to it of course, but you are right we very much disagree on this point.
And while I agree that there are time periods where historians are reduced to little more than conjecture when it comes to historical facts or how the people of said times lived, I don't think early 15th century is really one of those times, at least in Europe. There were plenty of people who kept records at that point, from monks to Italian bankers to actual historians, and Bohemia was an important enough country at the time that we should be able to have a good idea how people lived there.
There certainly are times where more and less records were created (and survived) but even in the times where there are many making certain that you've followed a thread which has solid backing and that such backing isn't distorted by contemporary bias (either theirs or ours) or outright misrepresentation (revisionist history has been around at least as long as Egyptian Pharaohs), is another thing again.
My dear friend, who is currently finishing his post graduate studies in history, has very firmly educated me during our semi-frequent discussions of history and culture, that making statements which are either too unequivocal or too confident is very likely to mean that you are making statements about history which are in some manner unreliable.
I don't claim to be an expert in the field by any means (I dabble here and there but am no professional) but when someone I trust who is a practitioner of the field tells me something I do tend to take them at their word.
That aside a lot of this seems to revolve once more around the our simple difference in perspective about the accuracy of a setting. To me a setting which is more like the historical context is more historically accurate than a pure fantasy setting which makes no effort to contain historical representation, but again from my perspective this is all on a spectrum there aren't really any binary answers to be found here (well, okay, something set in the future isn't historical... unless it's A long time ago in a galaxy far, far away.... then maybe ;) ).