Really I think Apple shouldn’t have released the 2020 Pro at all. The poster has a point in that you would expect the Pro to unquestionably have the best processor at all times. Pros had A9X and it took until 2017 for the standard A9 to go into the base model, and once the Pros went A10X it was the best part of a year before the A10 got to the base iPad. The Air 3/Mini 5 getting the A12 in 2019 took everyone by surprise, as the gap was shorter still.
I don’t think anyone expected an upgraded Air to get the 6th/7th Gen treatment in using the same processor, so it was always going to be ahead of the Pro A series wise. I think the A13 was expected, so this was always going to happen as an A13X doesn’t exist. Again the Air was given more of an upgrade than anticipated, causing Pro owners to feel short changed. That the Air gets an A series that hasn’t even launched in the flagship iPhone rubs more salt into the wound - why would they not launch a new chip generation in a ~£1000 iPad then?
As I think I’ve said before, I don’t think Apple will now sell many 2020 Pros. This might be why it seems to be the only iPad now getting the free AirPods. People will buy the Pro 2018 or the Air 4, or wait for the next Pro.