I think a real fundamental issue (and one that has led to major Apple blowups before too, albeit impacting fewer users) is that Apple made it a zero-sum game unnecessarily, and one not following a strict-superset pattern. They forced an either-or adversarial situation, which of course will drive up emotions more since it by definition dramatically raises the stakes for how useful the new thing must be.

It's true that simplicity is itself a virtue, and cutting old stuff is often at least as important as adding new stuff. It has too often been the case in the tech world that there is always a push for adding new features but not for subtracting old ones at the same time. This has and will continue to cause anger and has been a bone people have picked with Apple since the start of the modern era with the iMac, yet has served them well.

However any virtue can be taken too far or become a bromide, applied as a superficial cultural practice without an understanding of the foundation that previously made it work. Take Apple's aggression on ports for example: a lot of people are (with some justification) upset about having all TB3 ports and thus needing a lot of adapters for older gear. But at the end of the day TB3 is a superset of what came before and then some, it can do everything the older ones did, and the USB-C form factor is genuinely good. How exactly that plays out long term and whether 10 years later everything uses it and it will have all been worth it can be debated, but nothing is lost. But the touch bar simply lacks the features of tactile feedback and muscle memory the function keys offered, so it's not a superset, it's a tradeoff. It offers something new, but it also takes something important away. So whatever is new can't just be "oh that's kind of nice sometimes" and get an easy on-ramp with users, it must immediately be so good it justifies losing what they had before. The Touch Bar doesn't meet that standard, and worse suffers from the fundamental issue of attention requirement. Granted it's not entirely useless, but I don't see how it could ever meet the same ROI particularly for a pro system given that it doesn't really seem to support productivity scaling.

Going back to the start the big tragedy is it's not as if there isn't plenty of vertical space in even a 13" (or 11" for that matter) system on the opposite-screen surface. There was no need to get make it zero-sum, they could have just offered the Touch Bar as a new feature above the function keys. If they had all the angst would have been avoided, it would have been something cool and occasionally useful, and since nobody would lose anything that's all it'd need to be to justify itself. Sure there'd be some grumbling about BOM but that's pretty minor in the scheme of things for these systems.

Incidentally I think this same effect has happened elsewhere for Apple. Consider the reception of the Mac Cube vs the Cylinder Mac, which was effectively the Cube 2. Both tried to do an Apple take on an SFF system, which in the PC world are quite popular, and tried to cram a lot in. Neither ultimately was very successful. But the Cube had some fond users and was generally regarded as "well that's pretty neat even if I don't want one", whereas the Cylinder was awful. I think that's because with the Cube Apple kept the Power Mac. Nobody was forced to use it, so only those who wanted it's unique tradeoffs got it and everyone could be happy. If Apple had killed the Power Mac and said "oh yeah the Cube is totally what all you want" the reaction would have been at least as much (or more) then what happened when they killed the Mac Pro. I appreciate what a horror the 90s were for product line proliferation, and I still hate going to a lot of OEM sites and trying to navigate their multi dimensional product matrixes and a hundred minor variations of the same basic thing. But Apple has cut so much that they've reached meat and bone in some cases and have created problems for themselves unnecessarily and without getting any payoff in return.