You must have missed the research part. Nothing in that about personal preference. Research has shown kids start learning at a very young age, if you hold them back from academics you set them back and reduce future potential. Now that does not suggest a gap year would hurt or maybe not even a 7th grade repeat. But holding them back from kindergarten, pre-school would. Its obviously not an absolute as certainly some parents could be home schooling while held back at a higher level than kindergarten, 1st grade etc. But how many holding kids back for wrestling, baseball etc are actually doing that? The ones I saw mostly thought their kids were going to get a free ride to college. College is about academics and learning so why would you do something to reduce their academic potential just to maybe save money on college when there's really no intent to go there for the academics.
Long response but if you don't believe the above I present my case study: the 3 Ferrari brothers.