Rather than looking at admissions selectivity percentages as a proxy for educational quality, I think it would be more instructive to look at other data, including the following “peer group” institutions as selected by institutions themselves.
https://www.chronicle.com/article/who-does-your-college-think-its-peers-are
“Custom peer groupings and institutional data are from the National Center for Education Statistics’ Integrated Postsecondary Education Data System for 2021-22. The peer groups are self-selected by the institution.”
Looking at three schools that have been discussed here and which all have sub-20% acceptance rates and top-25 US News rankings, there are a lot of peer institutions they selected that have higher acceptance rates than that arbitrary cutoff. If the schools themselves think that these “less-selective” places are peers, it might be worth re-examining the rigid list based on perceived prestige.
In addition to the standard Swarthmore, Williams, Amherst, and Pomona quad and other schools with very low acceptance rates, these other peer schools were chosen that have lower rankings/ higher acceptance rates:
Bates: Conn College, Dickinson, Franklin & Marshall, Kenyon, Macalester, Oberlin, Occidental, Richmond, Sewanee, Whitman
Carleton: Beloit, Bryn Mawr, Dickinson, Kenyon, Lake Forest, Macalester, Oberlin, St. Olaf, Wooster
Grinnell: Kenyon, Macalester, Oberlin, St. Olaf
As a bonus, most of these schools have swim programs that are less selective (except for Kenyon, Wooster and a few others).