It turns out that not all A15 Bionic chipsets are created equal. For some reason, Apple includes a weaker A15 Bionic in the iPhone 13 mini and the iPhone 13 than the iPhone 13 Pro and iPhone 13 Pro Max. Even the US$499 iPad mini 6 contains Apple's best A15 Bionic SoC, though.
https://www.notebookcheck.net/The-iPad-mini-6-is-the-cheapest-way-to-purchase-Apple-s-best-A15-Bionic-SoC.561883.0.html