Yep, it would be difficult to decide for sure. I actually recently upgraded from 2018 iPad Pro 11 inch to M2 iPad Pro 11 inch. I would not say that it is a must and everyone has to do to it but I do get some improvements - mostly in RAM management. The 2018 has just 4 GB RAM and this was just not enough for me. I historically have issues with this with iOS/iPadOS so no surprise there. My browsing in Safari would be quite often disturbed - sites crashes/reloads, sometimes sites do not load fully (for example Reddit).I get that feeling, when I am contemplating what the next logical upgrade from my 2018 iPad Pro would be (similar to my 5k iMac). An iPad Air would primarily be for the M1 chip, but is otherwise a downgrade in every other aspect (screen, speakers, camera). The Pro is pricey, and the M2 chip doesn't seem any better than the M1 (it might eventually?).
Another thing is that I had 400 GB stuff in my 2018 iPad and iPad Air with 256 GB just would not be enough to fit that.