You mean, where I said “a form of low steel” a couple of words before the parenthetical statement you quoted? Unquestionably, by the 17th century, European metalurgy was far more advanced than contemporary Japanese technology. However, swords no longer had the same role in Europe at the time in question. In fact, the longsword was all but gone by that time (surviving only as a martial arts weapon of a couple of schools, no longer a battlefield choice).
Early longswords used on battlefields, and later “civilian” versions, were typically 46-52 inches long and 2.5 to 4 pounds, as you note. Later military examples, used mostly from horseback, were typically 54-56 inches long and 3.5 to 5 pounds. A katana, which is a type of daito, was typically around 27 inches, although different swordsmiths had their own ideas about the “perfect length.” They were usually 2 to 3 pounds.
You’re right. What I meant but failed to express, is that they are designed differently. The edge of a longsword was forged as an axe, not a knife, because it relied on heft behind the blade to cut through metal armour. A katana, on the other hand, has a much narrower blade, more suited to slicing lightly armoured opponents than European warriors would typically be facing. It would be utterly useless against your average 15th century heavy knight. European swords designed for lighter armoured opponents were typically one-handed.
Good thing there are people like you around to correct me, then.