I think the Japanese faction should remove the tall, walkable stone walls. Based on Japan’s terrain, landscape, and resource conditions, it’s simply unrealistic for them to have such long, thick stone walls and massive gates. In addition, constructing such walls according to the varying mountain shapes and slopes would require large-scale filling and layering of soil.
So, the stone walls and gates should be removed, as well as the wooden walls and gates. Instead, Japan could have unique single-sided stone walls with shooting slits. Ranged units standing behind these walls could be given a small damage reduction bonus that doesn’t break game balance.
Alternatively, the Japanese faction could have its Town Center automatically placed on elevated terrain at the start of the game, and every structure they build could automatically raise the ground slightly — similar to how the House of Wisdom works. When these elevated areas connect, they could grant bonus hit points to nearby structures, which would better reflect Japan’s unique characteristics.
Of course, whether or not they adjust the terrain system doesn’t matter much — but I still think the wall design could definitely use some changes.