I don't see how any attempt to maintain any semblance of historical accuracy in a game like D&D that has magic, a large number of sentient species, and undead, higher beings, and even gods that many people in the world have experienced, often regularly.
This touches on something I realized a loooooong time ago. What you get out of
any system (not just talking about games, but anything describes as a system) depends heavily on what you put into it.
Clarke's Third Law states any sufficiently advanced technology is indistinguishable from magic. But equally true is this: any sufficiently dependable and inexpensive magic is indistinguishable from technology.
That means that the very magic that suffuses the structure of a medium to high magic RPG setting will perforce change the societies in which it operates. Most players (on either side of the screens) don’t start off thinking like this, but if they start examining the ramifications of what spells do and how common they are, they start to.
Example #1: why have torch or even gas style streetlights (depending on technology in your setting)- and a Lamplighter’s Guild when Continual Light is equivalent in lumens, is a first level spell that lasts until dispelled, uses no fuel, and is not
a fire hazard? Given a few decades, no human settlement would be dark at night. A few more decades, and
someone would make a flashlight analog more ergonomic than CL bullseye lantern.
Why? Realize that human beings are the key part of the equation. Because humans look at problems and try to solve them with the tools available,
someone is going to look at what magic does and spin out ideas about what you might do with it. Look at any group of experienced gamers and you’ll find a host of ways they’ve applied magic like a tool: mills run on waterpower from a Decanter of Endless Water or using constructs or undead instead of livestock to turn the millstones pop up with
alarming frequency.
Similarly, those humans must
react sensibly to what magic does within the world around them. The medieval society feared war, fire and pestilence in ways we really don’t today. But if you look at RPG magic and critters, the challenges presented are more akin to what we face in the modern world.
Example #2: medieval fortifications had to deal mostly with threats from humans, ballistic artillery, undermining, disease, fire and supply lines. Those factors determined how and where they were built. But in a medium to high magic world as depicted in an RPG, how many threats can you name that actually FLY or create tunnels quickly and ignore or destroy walls completely? How many ways can people in the setting combat fire, disease, starvation and produce drinking water?
So why should game fortifications resemble medieval castles? If you think about it, in a medium to high magic world, they shouldn’t.
And if the ruling class isn’t building mountains of carved rock in strategic but somewhat inaccessible locales with all those taxes they’re collecting, what are they doing with it?