USC doesn’t have a secret formula so once you are qualified enough, luck and timing play a role. If you look at their statistics and comments of past applicants, having National Merit can play for or against you. They limit NMS numbers to suit their available funding. Additionally, your odds of getting into other good schools and lowering USC’s acceptance yield can make you less appealing. Number and quality of applicants from your high school matters too, as well as percentage of enrollment to USC. If historically 50% are non serious applicants diversifying their odds, it plays against you.