I think that once you get into a certain selectiveness, it’s kind of a crapshoot. I got into Brown, but I got waitlisted at Amherst. There might be certain things that admissions officers are looking for in a class at one school that are overly abundant at another. It’s also possible that a school might deny a student because of yield reason (I think this is known as Tuft’s Syndrome?)
But I mean, there’s always going to be anecdotal evidence – “My neighbor’s grand-nephew’s third cousin’s aunt’s best friend’s daughter was a B-student, and she got into Harvard!” The truth is that everyone’s chance’s at school’s with low acceptance rates are, well, low. And the higher your stats are and the stronger your extracurriculars, essays, etc. are, the better your chances are. Which doesn’t mean that you have a “good” chance, but.