That would imply that GPA and MCAT are meaningless once you get a secondary, which is almost certainly not the case, especially considering the fact that most schools send secondaries to all applicants. As for the interview,
LizzyM compares it to being on a staircase. The people with the best applications are at the top, and those who barely got the interview invite are at the bottom. Your performance in the interview can move you up a few steps or down a few steps. After the interviews, those near the top get accepted first, and those still near the bottom start getting rejected. Your stats and application are still extremely important, even after you get an interview.