2016 was a bad year. New iPhone has been the worst selling one in relative numbers since the iPhone. New MacBooks has several issues and controversial choices, while not bringing anything substantial to the table. New Watch changes are so small, nobody noticed an update.
It's all relatively minor in isolation; voicemail consistently fails to load messages multiple times before it succeeds, voicemail occasionally crashes, apps get stuck halfway down the screen after I swipe to check the notification screen, texts and iMessages sometimes show up hours or days late, notifications appear on the lock screen but are missing when I unlock the phone, the weather app sometimes displays a blank temperature, web sites have broken behavior with auto-playing, the state of the device when using volume controls changes unpredictably, and so on.
Most of these are undoubtedly caused by my service provider, or a 3rd party app, or me fat-thumbing an interface, or my complete misperception of a UI paradigm, or are otherwise not Apple's fault. But that's entirely besides the point, because we're talking about my emotional reaction, not reality, and we're talking about something Apple used to bend over backwards to control.
If the common narrative about Apple's modern successes being rooted in design sensibilities is correct, I don't see them being able to sustain leadership in the areas where they've been leading. The good news for Apple is that there still aren't better alternatives for customers who are heavily invested in the Apple ecosystem. The bad news is that there eventually will be, and also that there is material economic harm in keeping customers but losing their enthusiasm.