The involved method of forging a good Japanese Daito was a requirement of the poor raw materials and outdated metallurgical methods used in Japan.
Europeans had used a similar process called pattern welding, but they abandoned it once better technology allowed blades to be forged from a single piece of material.
The difference in sharpness is mostly modern misinterpretation. Historical Japanese blades would NOT have the razer sharp edges you find in modern replicas.
It doesn’t matter that they aren’t meant to be used against armored opponents, in regular use the blade WILL make contact with other rigid materials, and a very hard, very sharp edge would only prove to be a liability.
The hardness and sharpness of the edge would have been similar between the European longsword and it’s Japanese counterpart. If the Katana was sharper, it would have been to a degree that would have afforded it no advantage in a real world scenario, vene if it could have been measured in a laboratory.
The European Longsword’s ability to take stress, btw, is NOT matched by the Japanese Daito. The different metals joined to form the spine and the edge and the resulting blade geometry made these weapons VERY rigid. If you did manage to inflict enough stress to significantly bend the blade, it was likely to warp and require repair.
Again, some modern smiths are using more modern techniques to create replicas, such as creating Katana blades that are much more like European swords, and flex and bend a lot like them, and not at all like a historical Japanese weapon.
The weight of both weapons was about the same, BTW. The longsword, however, was longer. This is a byproduct of the difference in blade geometries. The European longsword would have exhibited a LOT more distal tapering compared than the Katana, hence it was lighter per inch of length.
I would agree that the European longsword was the more versatile weapon. It was meant to be.
Finally, it’s wrong to say that the Japanese longsword was the primary weapon of the Samurai as this was NOT true until AFTER the samurai left it’s traditional role of the battlefield warrior. During the time of peace is where you see the cult of the sword take hold in the samurai class.
It’s also when the old samurai start making fun of the young samurai, who no longer fight on battlefields, but in dojos.