Darry certainly isn't a perfect leader, and lashing out at Ponyboy when he came home late isn't his best moment. And yet, he does show some good leadership qualities.
Most notably, Darry realizes that he's the central force in keeping his younger brothers together. Darry is intelligent, and he could have gone to college. He's also handsome, and the group often refer to him as "Superman" and "Muscles." With all these things going for him, Darry has options. He could have chosen to leave his brothers behind following his parents' death and create a new life of his own. Instead, he chose the path of family responsibility, and he works hard at physically demanding jobs so that he can make enough money to keep his family going. Darry is seen in the kitchen, whipping up food for his brothers and friends. Darry dedicates himself to his family's well-being, and while this often leaves him physically exhausted and fairly ill-tempered, he's young and trying to find his way in the adult world of raising kids.
We also see a new Darry emerging after the rumble when Randy stops by. He's open to this Soc (a member of a socioeconomic group in the novel) visiting his younger brother but hangs around to keep a handle on the conversation. When Randy mentions Johnny's death, Pony starts denying that Johnny has died. Darry calmly tells Randy that it's time to leave and then makes sure that Johnny isn't smoking in bed. His demeanor has changed, and his calmness during a tense scene shows Darry's growth in leadership potential. There is a sense that Darry has reached a new maturity himself and will guide his younger brothers with a more patient and gentle leadership.