I agree with @tsbna44 about there not needing to be a specific number of schools in each bucket. A school’s admission rate is a correlation of how popular a school is in comparison with how much space it has to accept students. There are excellent schools at all levels of selectivity and there is no requirement to have schools with low odds of acceptance on a list. The only category that I strongly urge applicants to have at least two schools in is the Extremely Likely category to ensure choice at the end of senior year.
In terms of how an applicant’s list is balanced, one thing I think is important to consider is the applicant’s mental and emotional makeup and how they handle rejection. For some people, rejections are like a fuel that they use to be even more awesome wherever they land. For individuals like that, a reach-heavy list can make sense. For most people, however, rejections are a mental and emotional blow. I find that most people do better with more acceptances than rejections. So for a kid that tends to handle rejection more like “most” people, I would be likely to have a list with more toss-up, likely, and extremely likely schools than lower and low probability schools. But again, this is very individual-dependent and not a one-size-fits-all situation.
Additionally, I believe that a school should only be on a student’s application list if they are happy to enroll and attend for four years and there is a path to affordability. So I would not fill up a list with tons of extremely likely or likely admits if a student would not be happy to attend there come spring of their senior year.