The katana is an excellent cutting sword; in my opinion, it's the best cutting sword in the world. The flaw in its design is common to all cutting swords: even with its sharp point, the katana is useless against rigid body armor. That is why the katana, like most swords, was a secondary weapon. The samurai's primary weapons were bows or spears.
It ain't the sword itself that's dangerous. It's the asshole holding the sword that's dangerous!