Sonny had some of Vito's characteristics just like all the kids did. None of them was a duplicate. Yes, Sonny's temper led to rash and counterproductive actions. He wasn't a long term thinker. As it says in the novel, he would guard his father's empire until his father could take the reins again. it also says he was a brilliant battlefield tactician and won brilliant vistories. But it also says that he lacked the long-term strategic thinking of his father. He was band-aid.