Katanas, and other Japanese swords of similar construction, are not as optimized for making the best cut as possible as many people believe, but they do have characteristics that aid in making a good enough cut, even though other swords theoretically could cut better.
Even a glance at a cross section of a katana would reveal that they’re really wide and steep for a sword that is specialized in cutting, and would have to push more material at a time out of their way.
“But wait,” say the katana fanboys, “their wideness makes them stiffer.” Breadth of a blade keeps it from flexing away from it’s target, meaning less energy is wasted flexing the blade. Width keeps the blade from twisting to the left or right and being deflected, but with a good grip and good edge alignment the forces twisting the blade to the left and right should be almost equal, and with perfect edge alignment, there would, hypothetically be no more force pushing it to the left or to the right than there is to the other.
“But katanas are curved,” the katana fanboys desperately retort. Curvature of a blade only aids in cutting capacity, because it can lessens the amount of blade that is being forced in at a time. The curvature of a katana is so minimal that even when performing a draw cut it causes negligible difference in cutting performance. The slight curvature of Japanese Katana-like blades or of European sabres isn’t enough to greatly increase their ability to cut, but does aid in edge alignment, because similar to a wiffle ball, the trailing side will naturally tend to stay as the trailing edge and the leading side will tend to stay facing forward.
“But katanas have hard edges!” The katana fanboys say as their last defense. A hard edge does not mean that edge will be sharp, it just means that it will be easier to keep sharp. Even a piece of wood can be made dangerously sharp, it just generally wouldn’t be durable enough to stay sharp after much use.
I’m not saying that katanas are trash, but I would argue that katanas are not optimized for giving the finest cut, but rather they’re easy to give a good enough cut with.
Scientifically repeatable tests --as opposed to unscrupulously repeated tales-- only show katanas as able to cut through a thin, flat, piece of mild steel that is held securely in place, not cutting through other weapons and certainly not if the other weapon is in someone’s hand, where it would be moved away rather than deformed or broken.
This sounds cool, but basically no other sword design is put through these tests to compare, and cutting through carefully aranged bodies, at carefully selected points, with carefully selected techniques, performed by carefully selected professionals is not equivalent to some random account of some random person getting their sword stuck in real combat with bodies positioned in ways that they didn’t choose that are probably wearing atleast somewhat protective clothing, and were struck at the point that was available to be struck at that moment, rather than the area that experience had shown was a good place to cut through.