There are so many advantages on the Pro hardware over the standard 2017 iPad. Yes, it comes at a price, but I could never go back at this point.
Apple has done something that very much needed to be done in the iPad line: they've simplified it and given greater differentiation to the different models. If you had said last year that there wasn't much different between and iPad Air 2 and a 9.7" iPad Pro, I would have had a much easier time agreeing with you. As much as I loved my 9.7" Pro, I had a hard time recommending that model to anyone who didn't really need the horsepower, even though it had the quad speakers and the Pencil support.
However, now we have a Pro line that has its own set of screen sizes and features:
1) Fully laminated screens. The 2017 iPad doesn't have this, and it makes a big difference in both how it looks and how it feels and sounds when you tap on it. iPad Air 2 had it. 2017 iPad does not.
2) 10.5" size replacing the 9.7" size. On paper it doesn't sound like a big difference. Up close and personal, it's very different. Marketing wise, it also forces the consumer to take a second look at the Pro, where as before they might have said, "Meh, the iPad Air 2 is close enough and it's cheaper." Much less the case now.
3) Pencil support and ProMotion. Again, on paper, it sounds pretty "meh". When you see it in person, it's incredible.
4) Smart Connector. I don't care if the only things that ever take advantage of it are the Smart Keyboard and the Logitech case. It's a big deal if you want to use a keyboard with your iPad. No battery charging necessary, no finicky Bluetooth connection to deal with, etc. You just pop it on and start typing.
5) 4 GB of RAM, which is one of the biggest reasons I upgraded from the 9.7" Pro to the 10.5" Pro--it unlocks all the features of iOS 11.
I know that a lot of this stuff is only going to be noticed/used by power users, but isn't that the whole point? There is DEFINITELY more differentiation between the models now, and at the same time Apple has gotten rid of most of the old hardware (save for the iPad mini 4) that was cluttering up the product line. If you want an iPad, you get an iPad. If you want an iPad Pro, you get one of the two sizes of iPad Pro. If you want a small iPad, get a mini while they're still being made.
EDIT: I do hope they update the iPad mini 4 at some point. For the sake of consistency with what they've been doing with other models, they could just call it "iPad mini" and make it be a small version of whatever the standard model iPad is. Updates to the iPad and iPad mini would happen concurrently, and updates to the two iPad Pros could happen concurrently.