Now try to roll around with a longsword, a danish, or a big bad axe Urist, and you will see the difference in effectiveness.
I don't know anyone who is a consistantly better dueler than you, as I have to try 20 times to beat you when you fight with a 1hander.. I'm sure you are deadly with a Katana build, as with any build. Just try to see the difference..
It's short range forces you to block the first hit of almost any enemy you encounter, even 1handers, harder to cut down passing cav, reaching that guy following you etc etc. In battle, range is king, and it's important to make up for lack of range, to balance out the katana.