The difference being, in this case, that we know for a fact that the improvement from A7 to A8 is 20% and the improvement from A8 to A9 is more like 40%.
Yes. But there is no Mini with an A9, so the comparison is pointless.
You're forgetting that 1) They shaved down the size of the iPad Mini 4 even more (quite a bit more), and subsequently, 2) They under clocked the A8 in the Mini 4 (likely due to the former) which means they did, and probably will, run into cooling/throttling issues with equivalent Air quality (speed) chips in the Mini form factor.
Granted, with that said, I'm not sure why the iPhone 6 and 6 Plus don't have any problems with heat. Even though they're clocked lower, the surface area/space of the chassis is significantly less.
I want an iPad Pro.
However I want Devs to write apps and GAMES that take full advantage of the iPad Pro.
Do you think this will happen?
I highly doubt it. For several reasons. First the most obvious; it's just another iPad. If people didn't do it already with great chips like the A7X (and they didn't really), they won't do it now. Second, the market for the iPad Pro is going to be super small. Especially with the Air 2 looking like a great deal for a more "reasonable" form factor, hardly anyone is going to have a Pro unless they're a techie or professional.