Also, at the time of his first appearance, Luke was still being played by Christopher Tavani, and, therefore, much younger than Karl's character. This was when Will had just been released from prison. Will saved Luke from his bullies at a time when Lily was trying hard to get Will locked up again (as she couldn't forgive him for murdering her sister).
About a year later, Luke has been SORAS-ed (with Jake Weary, then Van Hansis) and started hanging out with Kevin.
Killing Dina is such a stupid idea. The Abbotts need her and the show needs Marla Adams. JG has no idea what he is doing at this point and Anthony Morrina is not exactly helping things with his 2007 GL aesthetics.