Darth_Glentract
The Truest Sith Lord
If Luke had wanted, he could have instantly killed Welk and Lomi Plo with his emerald lightning. He decided not to. He gave them a chance for as long as he could.
The main thing you have to consider though is that Jacen is family. Jacen is Luke's nephew. I recall Luke freaking out when he thought Jacen was dead as he had already sent one of Leia's kids to his death. Luke's not going to do that again.
How about you go ahead and quote the part in Betrayal where the fight was, as I'm having trouble finding it. A page number or something. When you have that, tell me which words lead you to believe that Luke was giving it his all.