Any Jedi could kill a Dark Trooper easily. Luke never killed one 'cause he never came across one. And having killed more Jedi (yes that is the correct plural) says nothing about one's skill. All the Jedi could have been very weak.
For Syndrix: It's very easy to use force destruction in a positive way. For example: If some Stormtroopers are shooting at some civilians, and there are too many too get all in time, you could use force destruction and be protecting all the civilians lives, and your own by removing the threat. Being a Jedi on the Light side doesn't mean you can't kill, it just means that you have to use your powers wisely, never kill with vengeance, or out of anger or hatred or any evil. When Yoda says only kill or use the force in defense, you can be defending anything, whether it's a person's future, or their life.
"Shut up Arcturus, if I wanted your damn opinion I would have beaten it out of ya." - Former Marshal James Raynor