If you’re asking about the performance, your original 9.7” iPad Pro has an A9 and 2GB of RAM (if I recall correctly), and the iPad 9 has an A13, which is a big jump in performance, and 3GB of RAM. On iPadOS 15 it’s very power efficient. I don’t know the battery life on iPad OS 16 or newer.
As for the screen, keep in mind that your iPad Pro has a laminated screen, and the iPad 9 has a non laminated screen, although it’s very comfortable PWM-wise.
I would try to go for an iPad Air 5, specially when the 6 gets released in October, and see if you can use it, because it will have a much longer and better lifespan.
Sorry yes I was just talking about the screen, it burns my eyes immediately.
Will do some research and wait for the new ones to be announced before I make a purchase.
Cheers