My daughter found herself in the same situation after 8th grade. She did her ninth grade year at a very prestigious exam school in New York City and re-applied as a repeat 9th grader. She’s now in her third year at one of the top boarding schools. After being waitlisted at 3 schools and rejected at 2 she was accepted at nine schools as a repeat ninth grader. Now please keep in mind she was in the top 1% at the exam school and a two sport athlete so there are more factors at play than just the repeat aspect of her application. Socially she is doing wonderful at her new school and her additional maturity is putting her in line for leadership opportunities. Best to you in your search and in my opinion you can only benefit from an additional year of school.