I'm running a Logic set up on my 2012 MBP, and I've never felt limited by its capabilities. I've been running Macs for music production for almost 20 years, and in my experience they have all at some point not had quite enough in the bag to let me do what I wanted of them. This is the first one (now fours years old) that has stayed ahead of my needs. I can run multiple copies of Massive, and rows of Waves plugins no problem.
I have hit limits with real-time 3D stuff, like gaming and Houdini, but music production is still well within its capabilities for me.
The people who make film/game soundtracks need a LOT of ram, and fast disks, because they're using terabytes of samples in each project. Also massive has pretty low requirements.
The main gripe musicians have with apple is the new OSX breaking their setup every year. The sandboxing in el capitan was particularly disastrous.
It sounds like you're basing this argument on hearsay and not personal experience (shocker.) I have various audio setups with different macs and interfaces and no OS update has broken anything with my setups since 10.6 era.
I don't think that's fair. Even major audio companies were warning customers not to upgrade to Sierra for months due to compatibility issues. Here's iZotope's page about compatibility with their audio plugins - if you bought it more than a couple of years ago, it won't work on Sierra:
Personally I had to spend a few hundred dollars upgrading my audio software that worked in Mountain Lion so it would run on El Capitan. I'm still running into a few glitches in places.
That page indicates what versions of those plugins are certified by the vendor to run on Sierra. That doesn't mean that older versions won't run, it just means they haven't been certified to do so.
I've been running software on Sierra that is only certified by the developer for Snow Leopard through Yosemite, and it still runs just fine for my needs. Apple puts a lot of effort into binary compatibility.
My personal experience disagrees with you. Waves, Native Instruments, and others, have had various issues over the years with OS X upgrades. I have projects spanning several years that forced me to wait a revision or two before upgrading to ensure they would continue to load and mix down as intended.
That's fair. I definitely have done a lot of sample-based and multi-track audio work and again have never hit that limit (on this MBP). However I do agree that if you rely on 3rd-party plugins there is a crapshoot every year as to how long you have to wait before compatibility reaches 100% and you can upgrade your system without breaking previous mixes or set ups.
How many developers need more capacity than the new MacBook Pro but still less than the largest laptops offer? The few non-gamers I know who are still CPU/GPU-limited are using clusters of machines because no single machine is large enough and in most cases it's significantly cheaper to rent capacity for the few times when they need it rather than pay up-front for something which will be idle a fair percent of the year.
1. People whose needs are satisfied by almost any laptop with an SSD and semi-recent CPU/GPU.
2. People who need the absolute top-end system but can fit their work on a single machine (e.g. if you had a model which uses 20GB of RAM, a 16GB machine is unsuitable but a 32GB machine is fine).
3. People who have so much data / computation that no normal computer can handle it.
My gut feeling is that #1 covers most of the market and the question is really how many people fall into group #2 but not group #3, especially in the context of laptops where the ceilings are smaller on both the Mac and PC side. I would further expect that a fair number of the people in the second group are not running those workloads 24x7 and thus have a practical, often cheaper, option of renting an hour of time on AWS/Google/Azure/etc. when they need to do something and get the results faster rather than leaving their laptop running for a day or two — even the best laptop GPUs are smaller capacity than what you can rent on a server.
"Web developers" should compile a browser(like Chromium) every so often, to provide themselves a reminder of the massive gap between what they do, and what "developers" do. Those CUDA cores and more CPU are very important to non-web-developers.
Engineers, CAD, musicians, 3D artists all need more power than it provides and increasingly need CUDA cores.