Try being more aggressive. Just run right up to them and spam the basic attack; as long as you don't let up, they'll be caught in a looping stun animation and be unable to hit back. Enemies are very slow on the draw so it's very easy to hit first, and once you do, they almost never try to do anything to break the loop, so you can just keep mashing away until they're dead.
One of the dagger/bow classes has a skill that lets you roll, which you can then equip to any class that uses daggers. It's helpful for getting out of the way if anyone else decides to come in and break up your stagger party and will become even more useful as you come up against bigger enemies with more dangerous attacks.
