Sounds like you want to make these two swords basically equal, with one having more swing damage and one having more thrust. Would you also want the price of the katana to be reduced? As it stands now, the katana costs over double the amount of the bastard sword.
I would like to see the stats on the katana tweaked as well but it should remain a fast weapon, no less than 100 speed. The continually lowered thrust damage is unfortunate but I think the first thing that needs to be changed about the katana is that it needs to have +2 thrust damage when masterworked. Currently it is the ONLY 2 handed weapon that receives +1 thrust at max rank. Even the studded warclub gets +2 thrust when fully loomed.