While I get what you're saying, and agree as far as various "under the hood" things that could be done to make things a wee bit better, those tend to happen on a continual basis, and never more than for Windows 10.
Back to the "adequate" thing I'll make it clear: Every Windows since Windows 7 has been way, way more than adequate for any purpose I can think of for a home or business user. I think that Windows 8/8.1 were a disaster from the user interface perspective because Microsoft made the assumption that everyone would be using touch-enabled devices. You can tell that just from the way the UI was designed, and that was a fatally flawed assumption. It was also a tectonic shift away from how a great many things "had always been done" that just pulled the proverbial rug out from under those of us who had been using Windows for decades. It was still adequate, but I never adopted it because it made life significantly more difficult on several fronts. Windows 10 is, in my opinion, a very good wedding of all the things that had been good and that I liked in the UI prior to Windows 8 along with adopting the things that were good about Windows 8. The only thing I hate, hate, hate (but have adjusted to - and it's certainly not limited to Microsoft) is the god-awful UI trend toward "flat look." Aero was far, far better in terms of visual presentation and there's already been research that shows that individuals navigate flat look UIs at a significantly slower pace than those that have dimensionality to the presentation of buttons and other controls. I work with individuals who are visually impaired, too, and you can see this issue writ large when someone is relying on residual vision and hunting for something. The classic "Red close X" at the upper right corner of a window is no longer constantly red and the minimize/maximize/close controls really hide, and hide well, when they are not rendered as though they were actual 3D buttons on a 2D surface.
But, in the end, OSes are no different than any other consumer product. What we have to choose from is what the various makers make. I've said it before, and I'll say it again: An OS is not designed for you (where you is the generic you, not you personally). OSes have to be Swiss Army knife type tools where a multitude of users in a multitude of contexts all have to be able to do what they need to do and many of them also have to have their wants/desires met on top of that. This inherently imposes a number of competing constraints and the need for compromise to arrive at the end product. No one is likely to ever be 100% happy with an OS as a result.
Brian AKA Bri the Tech Guy (website in my user profile) - Windows 10 Home, 64-Bit, Version 1803, Build 17134
. . . the presumption of innocence, while essential in the legal realm, does not mean the elimination of common sense outside it. The willing suspension of disbelief has its limits, or should.
~ Ruth Marcus, November 10, 2017, in Washington Post article, Bannon is right: It’s no coincidence The Post broke the Moore story