That's hardly true for many of the Apple apps (go look at the iTunes UI archive) and many of the changes are of questionnable usefulness/coherence/consistency.

That's hardly true for many of the Apple apps (go look at the iTunes UI archive) and many of the changes are of questionnable usefulness/coherence/consistency. You are just more used to it and prefer the "airy" look. As far as I'm concerned, macOS has severely regressed and that's before considering 3rd party apps. Many of them do not macOS UI convention anymore (they became shitty anyway) and many others just use completely custom UI (both technical and look); to finish you have windows/linux ports that just have the chrome of a macOS apps but the whole UI is completely foreign and doesn't even try to fit in. If your use case fits narrowly into the confine of what software Apple produces, I guess you could loosely say that. But their continuity is only about a general look, sadly not how things work (or should work), not really that important in the end. The System Preferences re-design is precisely a case of looks over everything else (and previously it already had been downgraded, with sections/labels removed to make it look more minimalist). Apple makes fashion and like a shirt it will follow a basic pattern, but a lot of details change, and it matters...