Hello AH folks.
Understanding that I come from a lay-background and an understanding mainly deriving from the Korean Peninsula, one thing that strikes me as curious whenever one thinks of the medieval period in Europe is the relative prevalence of fortresses, castles, keeps, and the lot and the cultural imprint they left on their landscape. While there were certainly some exceptions (Mont St. Michel, or the *very* contemporary Neuschwanstein "Disney" Castle), the general imprint is of a weighty stone building, perhaps with wooden roofs or some adjoining structures, but where almost the entirety of the building is construed of masonry. The kind of castle that shows up a half-dozen times in Monty Python's Holy Grail.
On the contrary, surviving examples of castles in East Asia largely seem to buck this trend in favor of almost exceedingly ornamental, wood-heavy structures. The Hwasung Fortress in Suwon, South Korea is seemingly more practically designed, but still features very detailed woodworking throughout the structure. Similarly, the Sakura Castle in Japan is full of windows, but seems limited in its capacity to actually attack against an assault. Similar examples in Japan all look terribly vulnerable to a rock coated in burning pitch.
So, if my presumption on the relative lack of, and when found, lack of *martial* (but not architectural) sophistication is correct, why did Korea and Japan, and perhaps China as well, develop complex Medieval-style societies with a variety of internal warring periods, not see the same need for massive as the Europeans did for large, stone fortifications? Were those that were built made more in the Neuschwanstein style, to project an image of wealth, harmony, or power by making ornate wood and shingle architecture?
Would leave to hear more about this.
If you'll pardon me for saying so: You're over-focusing on the structures and missing other defensive arrangements. The following posts should go some way to explaining the military and defensive value of Japanese fortifications.
I'm afraid I do not currently know of any posts re the Korean side of this question, so more can be said from anyone with the knowledge. (Both Japanese and Korean fortifications; all insights are equally welcome.)