I really don’t think that’s how admissions work. Admissions committees, for the most part, aren’t looking at an application and comparing it to the rest in their pile. Otherwise, how would they start the process? They are evaluating an application as an individual and asking questions like “does this applicant seem mature/nice/interesting/talented/etc?” before advancing them to another reader for more notes.
There are plenty of kids at every school who never re-class in 9th grade. If you (or your kid) were waitlisted, assume that the application was evaluated as an individual, and that application made it through at least one read by a committee member. Remember, you can re-apply next year (including evaluating whether a reclass would be beneficial at that point) if you feel like that would make sense for you/your family.
I think the reclassing discussions on here are often viewed in terms of “would it increase my odds of acceptance,” which is a mistake. A better way to think about reclassing is asking yourself “would I/my kid benefit from another year of maturing before boarding school?” (Full disclosure: I have two kids who went through the process, neither of whom relcassed at any point.)