…what really is the historically-analogous period implied in the garden variety D&D?It's an interesting question. The clues lead us all sorts of contradictory directions.
Which is all well and good, until you start talking about druids, large and unexplored frontiers within walking distance of the civilized world, feudalism, and the absence of gunpowder. These aren't even the trappings of the high Middle Ages of the 12th century. Most of these belong to the dark ages between the fall of Rome and the rise of Charlemagne.
It gets even worse when you start poking at all sorts of assumptions that the players have. Private rooms at the inn? Even as late as the American Revolution you're more likely to end up with up to eight people, mostly strangers, in a single room and in a single bed! Homes with glass windows, wooden floors, fireplaces, and separate, private bedrooms are also completely modern. The attitudes of most, especially in "good" lands, directly adhere to what we expect to find in suburbia, except with less football and a greater reverence for monarchy.
And why the heck not? Rigorous historical play can be fun, but that's usually not what we're about in these games. Letting our cleric of Bast and her kung-fu monk best friend go mano-y-mano with a high priest of Cthulhu for the broken shards of Excalibur in a back alley of Sanctuary while the city is under siege by an army of Barsoomian apes under the sorcerous command of Yyrkoon of Melnibone is just fun! Sometimes, what you really want is the no-time that is every time implied by the old Deities & Demigods book. If D&D truly has a default setting this is most assuredly it.
Art by Vittore Carpaccio and Frank Dicksee.