>The amazing thing about katanas is not that they're better than european swords (they're not), it's that they were able to make good weapons at all out of shit-tier iron.
How are they not better? I'm pretty sure European swords never had that neat feature of higher hardness at the blade than at the back side, giving the sword better strength while still staying sharp on the cutting edge.
Katanas are really different swords from medieval European swords, designed for an entirely different type of fighting. European swords are a product of the type of warfare they waged, which involved a lot of metal armor with knights. A katana wouldn't work too well here, so European swords are designed to crush armor and to be good at stabbing straight through the armor. Katanas were designed to use against unarmored or lightly-armored foes (I think Japanese samurai armor was basically leather), and are designed to be used in slashing motions more. I'd say that for their purpose and their style of fighting, katanas are definitely better. But against heavily armored opponents, they're just not the right weapon.