My daughter was accepted this year as a repeat Junior to a HADES school. They accepted 17 Juniors (but 44 Sophomores to give an idea). She is young and even though she is repeating a grade will be 18 when she graduates. The schools she applied to said they accepted Seniors, one said they took about 3 the previous year and another said they didn’t actually accept any, they were all PG’s.
I would say you definitely need to excel in everything as far as the application goes, grades, test scores, interviews, essays. And well-rounded is good but you also need a hook like varsity athlete, or something that stands out in the arts.