Most slashing swords are stopped by thick armour, that’s not unique to katana. Katana were plenty sharp enough, brittle metal tends to take a sharp edge, their weakness was mostly durability.
Heck, in Europe, if your opponent was wearing armour, it wasn’t rare to grab your sword by the sharp bit, and bludgeon them with the cross-guard.
Or fight half-sword (Halbschwert), you grip the blade with your free hand around the middle to deliver stronger and/or precision strikes against weak points in your opponent’s armor.
Most slashing swords are stopped by thick armour, that’s not unique to katana. Katana were plenty sharp enough, brittle metal tends to take a sharp edge, their weakness was mostly durability.
Heck, in Europe, if your opponent was wearing armour, it wasn’t rare to grab your sword by the sharp bit, and bludgeon them with the cross-guard.
Or fight half-sword (Halbschwert), you grip the blade with your free hand around the middle to deliver stronger and/or precision strikes against weak points in your opponent’s armor.