Once most business software has a cloud equivalent that can run via an internet connection (Google is already trying to roll this out for gaming, wrong direction of course), Windows and Mac are finished.
Once Windows and Mac are finished, it'll only be a matter of coming up with a new phone os that can run on 50-100$ devices (or android, yuck) and then Apple is really finished.
Who's going to spend 2k on a macbook, 1k on an iPhone and 500$ on a watch, when you can have a 200$ computer, 100$ phone and 50$ watch that do nearly the same thing. Oh, and a 200$ point-and-shoot camera that'll forever beat any phone-camera due to camera size limitations inherent to phones. In fact I predict the next big consumer hit will be a point-and-shoot camera with a phone os.
Microsoft knows this, Google knows it too - they're building out planet-wide infrastructure for cloud-first computing that's coming. Apple is jerking around with 0 progress on all of its platforms, milking brand loyalty, producing pretty, severely over-priced trinkets (awful battery life, awful keyboards, awful screen burn-in, insane ssd prices, awful ports requiring insanely over-priced adapters) to signal allegiance to a middle-class or up caste, and making their shareholders short-term rich, while long-term poor.