I think it needs to be made clear that Tolkien's Middle-Earth isn't, and wasn't intended to be, based on high medieval (which is the period most modern readers associate with the term "medieval" and the period I think is most relevant to this trope) Europe, but rather early medieval (often still called "dark ages") Europe. In particular, as the naming convention used for Rohan illustrates, Tolkien drew a lot of inspiration from Anglo-Saxon England. Tolkien was after all a scholar of Anglo-Saxon literature. In fact, many readers have concluded that Tolkien was, at least to some extent, attempting to create a kind of replacement for England's "lost" Anglo-Saxon "mythic memory", based on a letter in which he wrote "[England] had no stories of its own, not of the quality that I sought, and found in legends of other lands". The fantastical elements drew heavily on pre-Christian European mythologies and folklore, the best known sources being Beowulf, Norse mythology and the Finnish epic Kalevala (Tolkien expressed a particular love for the myths of Northern European peoples).
I think it needs to be made clear that Tolkien's Middle-Earth isn't, and wasn't intended to be, based on high medieval (which is the period most modern readers associate with the term "medieval" and the period I think is most relevant to this trope) Europe, but rather early medieval (often still called "dark ages") Europe. In particular, as the naming convention used for Rohan illustrates, Tolkien drew a lot of inspiration from Anglo-Saxon England. Tolkien was after all a scholar of Anglo-Saxon literature. In fact, many readers have concluded that Tolkien was, at least to some extent, attempting to create a kind of replacement for England's "lost" Anglo-Saxon "mythic memory", based on a letter in which he wrote "[England] had no stories of its own, not of the quality that I sought, and found in legends of other lands". The fantastical elements drew heavily on pre-Christian European mythologies and folklore, the best known sources being Beowulf, Norse mythology and the Finnish epic Kalevala (Tolkien expressed a particular love for the myths of Northern European peoples).