I'm not sure my text page numbers match up exactly with your version. Those page numbers do match up closely with my version's chapters 5, 6, and 7, so I will use those.
One positive leadership quality about Simon is that he has a clear vision and knowledge of what is right and wrong. That's true of him throughout the novel. He is the only true, innately good character. He's not good because adults told him to be or because he's being forced into it by rules. He's good, because he knows it's the right thing to be. Because of that, Simon easily can recognize right, wrong, good, and evil in other people. Near the end of chapter 5, Ralph is doubting whether or not he can continue being chief or even if he should continue being chief. Simon has been mostly silent, but he finally responds to Ralph's thoughts.
“Piggy’s right, Ralph. There’s you and Jack. Go on being chief.”
Simon knows that Ralph is still the best choice. Being able to recognize good from bad in himself and in others is a positive leadership quality.
A second positive leadership quality about Simon is his confidence. He is confident in himself, and he is confident in others. Simon is especially confident in Ralph's future success. In chapter 6, Ralph is again questioning whether or not the boys can actually survive the island until rescue. Simon responds by saying “You’ll get back all right.” There's no question that Simon knows this. It actually creeps Ralph out a bit, but the comment is so confident and truthful that Ralph is reassured. Simon also shows confidence by going out to explore multiple times by himself. He's simply not afraid of much. His confidence is a positive leadership quality.
A negative leadership quality about Simon is that he is frequently too soft spoken to gain control of and lead a group. Simon often fails to say anything at all.
Simon stirred in the dark. ”Go on being chief.“ ”You shut up, young Simon! Why couldn’t you say there wasn’t a beast?‘
In chapter 5, Simon had the opportunity to help Ralph calm rising fears about a beast on the island. Simon didn't say anything. His inability to help in a group setting is a big negative. He is too easily pushed out to the peripheral.