Yes, in minor ways I already mentioned.
>Isn't that what usability and polish are all about?
Yes, and as I already wrote: "Apple has done that for both platforms.". You don't get a lesser Metal or a lesser APFS on macOS vs iOS, or less UI integration.
>I know, and that's why we all love Snow Leopard. Why the regression since then?
I'm not particularly fond of Snow Leopard over other releases, nor I see much "regression since then". There are several legendary Siracusa reviews until Yosemite (after which he passed the torch) here: https://arstechnica.com/author/john-siracusa/
Here's e.g. Mavericks:
Over the past three years, each successive release of OS X has found its way onto all of my Macs in less time than its predecessor. This year, I may have already gone Mavericks-only across my whole household by the time you read this. Barring any unforeseen bugs or compatibility issues, Mavericks seems like a no-brainer upgrade to me.
And here's Yosemite:
Viewed in isolation, Yosemite provides a graphical refresh accompanied by a few interesting features and several new technologies whose benefits are mostly speculative, depending heavily on how eagerly they’re adopted by third-party developers. But Apple no longer views the Mac in isolation, and neither should you. OS X is finally a full-fledged peer to iOS; all aspects of sibling rivalry have been banished.
Do you see much talk about regression there? There are also post-Siracusa reviews on Ars for each macOS release up to and including Catalina.
>They release updates alright, but what about the quality? The fact is overall, macOS has gotten slower, buggier, and uglier with every release.
Uglier is pretty subjective if not downright wrong. The new dark mode is great, and the UI is as good as ever. What was better? The skeuomorphic years? The candy colored Aqua years?
Slower is easy: it's 100% wrong. In fact, can you show any number of it? If anything, memory compression and battery savings in recent releases made the macOS more performant, and dropping 32bit apps (and double-loading of the same libs for 32/64) even more so... And APFS is also a big improvement over HFS, and Metal is faster than the previous stack and has already given significant performance boost to FCPX and other apps.
I'm not sure what exactly you find "slower" then...