Look at the early Air vs. the 17" MBP. The 17" MBP had an actual expansion slot (expresscard 34), which you could use for stuff like eSATA adapters. It had Ethernet and firewire. It had lots of ports, and an optical drive. You could replace and upgrade the hard drive and memory. The Air? I don't think anything in it was swappable, never had Ethernet, only had two USB ports, no expansion options.
There was very significant differentiation here; one machine had many more options than the other.
No. The MacBook had USB only, the MacBook Pro had multiple other ports. The MBP also had the option of a high-quality antiglare display, which is a major feature for a lot of pro users. (In fact, most users are consistently happier with antiglare displays than with glossy displays; glossy displays look better in the store, but long-term satisfaction tends to favor antiglare. Glossy displays cause eyestrain and headaches.)
Now, the MBP has basically the same ports as the MacBook. It has more, but there's no longer the differentiation of having multiple different kinds of ports to allow you to hook up to stuff directly. It doesn't have the SD card readers that they had for a while. No expansion slots. Also no longer user-serviceable in any way. And that's a horrible thing in a high-end pro-grade laptop, because the ability to upgrade or replace RAM and storage is of significant value to a lot of users. A ton of people bought RAM or hard drive upgrades a year or two after getting the machine; that's a big part of why Apple laptops used to have a 5+ year workable lifespan. If newer MacOS needed more memory, you could upgrade memory. Disk filled up? Get a bigger disk.
If it's exactly what you want, you are in for disappointment. Why? Because they've been consistently trimming the top end. Every time around, they look at the people at the top end of the curve, realize there's not enough of them to justify things, and trim things a bit further. So if it's exactly what you want, then probably 95% of the users don't need quite that much. So next time around, you're in the top 5%, and you get cut out because making a machine that's a bit less than what you want would be cheaper, and still serve 95% of the customers just fine. And then, of the people who are left, they look at the top 5%, and drop what they wanted, too.
Furthermore, I think you're underestimating the long-term ecosystem impact of driving away the people who wanted more from a machine.
Apple used to at least vaguely cater to power users, and had "it's actually Unix, and you can develop stuff for it" as major selling points. Now, the default for app installation is to require developer-signed packages, meaning that you have to pay money to be a developer to distribute software that other people can use and install without a lot of hassle, and they don't cater to power users at all.
For that matter... How many people do you remember ever complaining about magsafe macs not being able to run off of wall power with a working adapter? I don't think I ever heard of that happening. Not even once. I heard about failed batteries, occasionally, but they were rare. And so far this week I've seen 5-6 people show up here with 2016s dying because something went wrong with the USB-C charging option, and there's no magsafe.
One of my coworkers got my 2016 MBP, and it had a glitchy line on the built-in display, so he sent it in for repair, having been promised it would be "expedited". He sent it in on the 22nd. His replacement still isn't back yet. Apple used to be pretty solid about same-day turnaround on replacements. Why aren't they now? Because they can't swap parts. They have to get in a motherboard with the right combination of CPU, memory, and SSD. They can't swap out the one part that failed, it's the whole thing all at once. My spouse's MBP died Monday, I can't even get in to see people before Thursday, and we have no expectation that the machine will be repaired within a week or two.
That's not something I would regard as acceptable in a professional machine. I had to send in a Thinkpad for repair once. Called in (day one), got return shipping package and shipped the laptop (day two), they received the machine (day three) and sent it back with whatever part swapped, and I got it back (day four). I also used to do that with Macs. I took it for granted that any remotely reasonable repair would be on that kind of schedule, so I would have my machine back three days after I called in with a problem. Now, it might be over two weeks, because Apple stopped making an effort to make machines that anyone could support, including them.
I know other developers jumping ship over this. I expect more, especially if the 2016 continues being as prone to catastrophic failure as it seems to be.
Man, if only it were possible to design a machine based on having it work reliably and be maintainable, even if that made it a millimeter thicker.