To be fair, Apple's hardware has come a LONG way in the last decade. The iPad Air 2 has an A8X in it, which is basically based off the iPhone 6 processor and is about 1/4 the speed of modern iPhone processors. Trying to run any modern version of iPadOS on this processor is going to cause some performance problems.
The tablet/mobile space is changing much faster than the computer space. 10 years on a Mac is very doable (my old one from 2012 still works to this day), but on a tablet, these things just weren't powerful enough back then. They've come a LONG way in the years since.