Some of the old Pro features were better (like ProMotion and a better camera), but the old Pro had A10X. New iPad Air (and mini) have A12 Bionic. A12 Bionic (in the iPhone) is roughly 20% faster than A10X Fusion for CPU in Geekbench 4, although for GPU Metal, A10X Fusion is roughly 35% faster than A12 Bionic.
Old Pro had 4 GB RAM, which is what I expect for the new iPad Air, but we don't know that yet.
I am dumbfounded by the Air name. No reason to reuse it. Just make it a 10.5 regular iPad. The iPad line is as complicated as the Macintosh in the mid-90s... And of course no new iMac or iPod touch.