Play a fighter/thief or fighter/mage instead. They're almost as powerful as their kensai counterparts and they don't require a dualling. If it's the vanilla game you're playing, this is more than good enough.
If you want NPCs considerably strong, I'd recommend the Solaufein and Valen mods. Beware, however, that they'll easily outshine any protagonist you can pick, except an inquisitor or sorcerer, mayhap.
However, these are on the other side of the scale and will most likely tick you off with their overpowerdness. They even take the fun out of challengens like Eclipse party and final ascension battle.
