I don't mean new features, I just mean updates. On older devices, once they fall out of support, the clock tends to start ticking for apps. Apps only support old versions of the OS for so long. Not saying it is the most critical factor, but when the discount for the old model is minimal (like it was when I looked) then it IS a consideration that is frankly more important to me than the hardware differences.
The OP said the difference was £200 - that isn't minimal. And I think, with respect, you are just digging in here for the sake of it. How likely is it, genuinely, that an M1 will become obsolete in such a manner that critical apps etc are not going to work for it, but are going to work for the M2?
To repeat what I said before - if the user is a pro (although I appreciate that word is often meaningless these days - and what pro really would use an iPad over a MacBook Pro??) then what is the likelihood that in 6 years time they will still be using an M1 iPad Pro as their main machine, and thus be threatened by some notional withdrawal of important apps?
They will have moved onto new improved hardware way before this would be a threat!
If they are a non-Pro, then the basic functionality of an iPad Pro will be unaffected - it will still do everything most users would need. I have the original 12.9 inch iPad Pro from Autumn 2015 and it still runs fine and does everything I need. If there was something that needed a bit of extra oomph then I'd run it on my M1 iPad Pro.