deeper there are lots of other subclasses.
Yale is number 1. Period. No one else is treated similarly. Harvard and Stanford are pretty comparable; they go back and forth in the rankings and generally have similar placement success. Chicago, Columbia, and NYU make up the next grouping. Then the next 6 are pretty well grouped together, and Cornell and GT round out the top 14. That doesn't mean there are 5 tiers in the top 14. The opportunities provided by a Yale, Stanford, or Harvard degree are massively different than those offered by a GT degree (just like you noted that a GT desgree is very different from a BYU or Utah degree).
The 4 tiers are just how the language has developed, but obviously that doesn't mean the schools in a single tier are all the same.