Look this is simple physics. The Katana is the lightest sword of that class and the shortest, it should have the best speed rank out of the bastard, hbs, and longsword. It should also have lower damages to represent the lighter blade.
If I swung two baseballs bats that both have the same weight except one was longer, I'd swing the shorter bat faster because it is more compact. The bastard sword currently has 1 more speed rank than the katana despite being heavier and longer.
Seriously change this weapon's stats. I know everyone hates the Katana and the weeaboos that use them, but the current system isn't realistic.