I just watched Malice a second time, and noticed something strange, after Simeon was on the planet when Rush and Scott were going after him.
Okay, first he takes a shot at Scott and misses. Then a second later he shoots a Kino, twice. You have to have pretty good aim to make that shot, in rapid succession.
Then, right after Rush's breakdown, when Greer found the footprint Simeon took several shots that all missed. The boys took cover, but in the view from Simeon's scope we see a clear shot at Greer's exposed head and chest... and still he missed.
Then he finally shot Greer in the shoulder, could've easily been a kill shot but wasn't.
Then Simeon gave his speech about wanting Rush to live so his pain would be worse than death, that explains why he didn't kill Rush but why not Scott or Greer? He ended it by saying next time he would kill Rush.
When Rush shot at him in the 2nd canyon, he turned and shot back a bunch of times, and missed -- not really keeping his promise.
So... why isn't he trying very hard? He clearly has no problem with killing people. He killed Perry just because she happened to be in Ginn's body. He shot and killed several people before he left the ship. He put a bomb on Park's back, another one in the rocks to try to kill Rush, and another one that almost killed James and her team. But when it comes to shooting people, he seems to not understand that it's his survival he's fighting for.