Building ecosystem of consumer and pro apps gave them a significant differentiation and was driving sales of hardware. In 2006 I bought my first Apple gear because of it (could have bought 2-3 PCs w monitors for that money). I started with iPhoto and 1y later I went for Aperture. In 2019 by killing photo apps, external monitors I have very little reasons to stick with them going forward when my gear dies. I already replaced my monitor with NEC and I'm using Capture One, which seems to run faster in Bootcamp than on OS X (same machine w eGPU).
If the only reason people are buying Macs is Apple’s proprietary pro apps, Apple is doing something seriously wrong. I am sure there are some people who bought systems to get Final Cut X, Logic, and/or Aperture, but that is a small part of their pro market. They have already announced that as part of the new modular Mac Pro, there will be an Apple monitor (or maybe monitors). It may be too late for them to keep you as a customer and that is completely their fault. However, it is their fault mostly because they have not been building compelling hardware for you, not just because Aperture is not supported.
Very few of 3rd party apps take advantage of Mac specific features because they strive to be cross platform. I'm not buying the argument of small teams - for some reason it is OK for them to keep engineers for audio and video pro apps, but not for photography.
Some (Affinity Photo, Pixelmator Pro, DaVinci Resolve,
etc.) do really take advantage of the platform. Again, they have sold 2 million copies of Final Cut Pro X, and (I would be primarily because of Photoshop and the Creative Cloud bundle deal) sold no where near as many copies of Aperture. Timing may have been an issue. Had Affinity Photo, Luminar and Pixelmator Pro been options when people were considering Aperture
vs. Lightroom/Photoshop, things might have been different.
I agree on the opportunity cost, but as a strategic decision this one was horribly wrong....seems to be a pattern since Cook took over. These software driven transitions happen slowly, but when they become visible in the financials it's too late to fix them.
There were just as many people screaming about strategic decisions that Steve made as their are about those that Tim makes. I understand what you think, and I do not have enough of the data to prove you are wrong, but I still think that the bigger problem is the hardware, not Aperture.
In my case killing Aperture is THE reason that my money won't go into Mac hardware or software after my current gear retires as I do not see any practical reason in staying with the platform.
It certainly is possible that even if Apple made hardware that was not very compelling for you, had they continued to update Aperture, you might have stayed. However, if they made hardware that was compelling now, you would stay even without Aperture. As someone at NeXT Computer, Inc. once said: “People should want to buy our hardware despite that it only runs our software, and our software despite that it only runs on our hardware. Our job is twofold: Make both so compelling on their own that they over come the downsides or their proprietary nature, and make the pair even more compelling.”
Apple’s more serious failure is not have compelling hardware for you (and others).
P.S. I am not trying to convince you that you should not be upset that it was your ox that was gored. I am just saying that, from the numbers I do know, Aperture was not a viable market for them.