You forgot, bezels and laminated screen.
Higher resolution?
iPad Pro 12.9 = 2732x2048, 264ppi
iPad Pro 10.5 = 2224x1668, 264ppi
2018 iPad 9.7= 2048x1536, 264ppi
Technically, yes there are more pixels on the Pro models. But they all have the same pixel density. Considering that all iPads share the same homescreen grid, single column widget screen (a step back from iOS 10's dual column on the 12.9), that extra resolution isn't always used to full advantage.
More RAM? (I think you meant more storage), but yes, the Pro's have 4GB RAM while the 2018 has 2GB.
Yes, you've compared the tech spec sheets of both the 2018 iPad and iPad Pros. I haven't seen anyone arguing that there is no
technical difference between them. What some are saying is that there is no a
practical difference for many. (Note: "many" not "all")
For those people who are more interested in "cost-value" rather than "premium", the iPad 2018 is very compelling. For many in that cost-value segment, TruTone, 120Hz refresh, and v2 TouchId don't attach a great monetary value to them. Camera, and smart connector, perhaps a little bit more.
There is a lot of buzz and excitement surrounding the 2018 iPad. It has caused a few of us, myself included, to ditch a Pro for it. Apple has done little in iOS and software to fully exploit the capabilities of the Pro hardware. That might change, it might not. Apple's attempt at the Files.app (simply their version of Documents by Readdle) shows me how little they are interested in moving things forward. Should that change in the future, I'll go back to a Pro.
Having said that, this is not to say that one choice or the other is more "virtuous". It is not more honorable to choose cost-value over premium. It's a personal preference. Hopefully these discussions help folks sort out which camp they'll be more comfortable in.