I guess the only plus for the air is the updated processor. Having compared my 2018 iPP alongside my older 2017 iPP (10.5) I found that they both did everything pretty much at the same pace and with equal efficiency. On a performance level the 10.5 pro and air 3 should be equally comparable imo.
other than the previous gen processor (A10X) the 10.5 iPP is a no brainier imo. Given the processing is similar, the extra ram (pro) and with the introduction of iPadOS, it’s safe to assume they will both be supported in future updates similarly. The 2017 pro is an upgrade in every other category to the air3.
I’ve sold my 2017 pro now but if I were to buy an iPad today, and of all models currently available, that’s the one I would Re-purchase. The quad speaker setup, Pro-motion with performance that matches current gen (2018) pro’s make it, imo, the best bang for buck. I don’t pay much attention to those that say the Air 3 will be supported longer. I’m sure They will both see iPadOS updates to a similar timescale