Even in selectivity (which seems to correlate strongly with overall USN rankings), the spread among top ~40 LACs is narrower. Between Williams and Mt. Holyoke, the difference in average SAT M+CR is about 110 points. Between HYP and BU, the difference is more than 200 points. Between HYP and UC Irvine, the difference is more than 300 points.
Rather than fret over the “Ivy League of Liberal Arts Colleges”, it would be more meaningful to identify which national universities provide the most LAC-like attention to undergraduates.