"As a sword, the Japanese katana is unmatched in its sharpness and cutting power. Furthermore, it is particularly good at cutting against metal (–but no, it only cuts through other swords in movies and video games!). However, Medieval plate armor is well known for its resistance to cutting, and cutting at a moving target hidden by a shield or a greatsword is not easy. While the edge of a katana is very strong with a sharp cutting bevel, it is a thick wedge shape and still has to move aside material as it cuts. Though this is devastating on a draw slice against flesh and bone, it is much less effective against armors. Realizing this several styles of Japanese swordsmanship devised specific techniques not to cut at armor, but to stab and thrust at the gaps and joints of it just as the Europeans did against their own plate armor. Except for major interaction in Korea and encounters against the Mongols, the katana developed in comparative isolation and is not quite the “ultimate sword” some of its ardent admirers occasionally build it up as. The katana’s exceptionally hard edge was prone to chipping and needed frequent re-polishing and its blade could break or bend the same as any other sword might (...and no, they won't slice through cars or chop into concrete pillars either). It was not designed to take a great deal of abuse, and is not as resilient in flexibility nor intended to directly oppose soft or hard armors as some forms of Medieval swords had to be.
The katana’s design was not set in stone. It was changed and altered over the centuries like any other sword, being slowly improved or adapted to the different needs and tastes of their users in terms of cross section, curvature, and length. In the 13th century for instance, their points were prone to snapping against the metal reinforced leather armor (so called "studded") of the Mongols and Chinese and had to be redesigned (essentially equivalent to European brigandine armor). By the 18th century their blades, no longer used earnestly against armor, tended to be made longer, lighter, and thinner for classroom practicing.
True, the Japanese feudal did have their own form of greatsword in the long no dachi blades, these however were employed specifically by lower ranking foot-soldiers against horses (and presumably, on occasion against pikes). So, we cannot draw an equivalency between these and Medieval greatswords used in knightly fencing arts or to the true two-handers of 16th century European battlefields.
Over all the katana was a very well-rounded design: excellent at cutting and slicing, yet good at thrusting, and suitable for armored or unarmored fighting on foot or horseback, either one or two-handed. It was a carefully crafted and beautiful weapon reflecting generations of artistry and fearsome necessity, but it was still only a sword –a man-made tool of well-tempered and expertly polished metal. Though the details of manufacture differed, they were made by the same fundamental scientific processes of heating and hand-working metal ore then shaping and grinding as were other fine swords around the world throughout history. Regardless of how they are designed or constructed, all swords have the same goals and perform the same functions: that of guarding against attacks while delivering their own lethal blows."
Extrait d'un article de J.Clément de l'Arma...
Pas le temps de traduire, désolé...
Alors, c'est sur, le Katana est bien beau, bien "Staïlé", bien tranchant, oeuvre d'art et tout et tout, mais bon, le coup de sa supériorité sur les autres lames européennes de l'époque tient plus du mythe de cinéma et de manga qu'autre chose...
Et il me semble que la technique de forge tenait plus à la pauvre qualité du métal au Japon qu'autre chose, mais il faudrait que je retrouve mes sources...