I am in audio, film and TV production and Apple has left us in the dust. This is because we need specialized components -- you can't just buy the computer ready-to-go from apple you also need to add stuff like a Blackmagic video card or Pro Tools HDX card (which doesn't have a thunderbolt version). This type of software used to be nearly mac-exclusive but the Pro Tools has seen a major shift to Windows in recent years because of the upgrade schedule/compatibility and lack of a modular machine.
In any specialized technical industry there is need to have specialized components and gigantic Sonnet Tech dongles for PCIe cards just don't cut it because they are added complexity. We grew up with tower computers, it can't be hard to just make a tower computer can it? There are thousands of companies that do it. I know 14 year-old people who can make a tower computer. It's nice if it looks good but that's so far down the list. A modern (and complete) set of ports is essential beyond Thunderbolt, PCIe, 5k Graphics. Aside from an SSD boot disk it needs room for 3.5" drive bays. It needs some kind of removable media, SD cards are looking good these days! Very widely used and getting better and better. It needs a combined analog/digital headphone jack AND combined digital/analog input jack for audio (many pro's use this!). It needs 2 10GB ethernet ports.
What I don't see mentioned much is that if a larger company (or higher-computer-need company, $$$ for apple) needs to buy apple servers they're also in the dust because there are none other than mac mini's. While a tower works ok for this, what's really appropriate is a rackmount server. This is a server that no-one ever sees -- it could be designed to look like poop and it will still sell because it is purchased for a specific need that winds up reinforcing the whole apple ecosystem.
Apple needs a Pro division with a lineup of chassis that they can keep upgrading without the design team involved that they can upgrade quickly to keep competitive with the rest of the world. Tower workstation/server chassis, rackmount workstation/chassis (maybe a 1u option and 3u option that can hold PCIe cards, eh?), 13" laptop, 15" laptop. Include Thunderbolt 3 yes but also SD card, ethernet and audio in/out on all (as just a slightly-overpriced option is great, even!)
The expensive computers wind up affecting the tablets and laptops on many different levels so neglecting them has left a big and long-lasting hole in the next phase of Apple because those server apps and audio/video production programs have migrated strongly away from Apple. These are the computer-deciders and content creators ... the mavens that are the word of mouth that worked so long in Apple's favor.
Design for the pro users could be so easy if you were to let go of trying to make flashy products for us and ones that JUST WORK. Let the consumers have the shiny stuff. Heck, the 'bulky' laptops could still have nice metal, the rackmount could look slick like a piece of audio gear. It won't tarnish the apple reputation in the slightest -- it will only strengthen it because the major holes would be filled.
One more thing ... the software upgrade codependency on OS has to stop! does iMessage really need the new OS to function? when it does, then don't leave the older customers out in the cold. Short term, shareholder wise sure it's what gets you a fat bonus but long-term health is a disrespect to Steve Jobs because the user experience suffers to profits.