I think it is okay to have ‘gap year’ as the safety. If the student really doesn’t want to go or couldn’t afford a school, don’t apply.
My kids were told to have 3 schools, including a state public school. They both had a top choice, applied early and got in on rolling admissions in Oct; they were done. I warned them that ‘something’ could happen, but they both decided they’d rather take a gap year and regroup than apply to schools they weren’t interested in. In the end the dream/1st choice/only schools worked out, but taking the gap year would have worked out too.