Tiers are a practical way of displaying rankings for optimal use on Draft Day. The goal is to accentuate which position is closest to a drop-off by denoting where the drop-offs are at each position. During the heat of the draft, you'll know that the position to target is the one that's current tier is closest to depletion.
For a deeper look at the catcher position, check out Scott's catcher strategies for 2022 here.
Note that at catcher, there is no Near-Elite tier, which would normally be second-highest. The talent doesn't diverge enough to justify the full allotment of tiers, and I do believe the drop-off from Perez is particularly stark.
The Elite: Salvador Perez
The Next-Best Things: J.T. Realmuto, Will Smith
The Fallback Options: Daulton Varsho, Yasmani Grandal, Willson Contreras, Keibert Ruiz
The Last Resorts: Mike Zunino, Gary Sanchez, Tyler Stephenson, Mitch Garver, Alejandro Kirk, Travis d'Arnaud, Joey Bart
The Deep-Leaguers: Eric Haase, Elias Diaz, Omar Narvaez, Sean Murphy, Carson Kelly, Adley Rutschman
The Leftovers: Max Stassi, Luis Torrens, Yadier Molina, Christian Vazquez, James McCann, Yan Gomes, MJ Melendez, Jorge Alfaro, Cal Raleigh, Luis Campusano, Austin Nola, Jacob Stallings, Tucker Barnhart, Tom Murphy, Danny Jansen, Francisco Mejia, Ryan Jeffers, Gabriel Moreno