[HoneyBadger]

the layers of steel do help, but the reason the swords are layered is to make the steel flexible while still enabling them to be sharpened to a razor edge, the edge being the more important aspect, because the sword needs to not only take an edge but hold it for a long time through severe but specialized use. They're really durable for what they're intended use is, but they weren't really made for cutting through heavy steel plate or shields or for directly parrying a Scottish broadsword, for example. You can turn blades with them, and you can cut through bamboo or even most kinds of armor, providing you have the skill necessary to use the blade correctly. Three blades next to each other would really reduce the ability to harness the skills involved. A katana isn't the weapon of a peasant farmer because the peasant farmer not only can't afford the sword, he also can't afford the time it takes to learn kendo properly.