In my experience Gnome is the worst major FOSS project for this. Ever since Gnome 3 the design philosophy of all of their projects seems to be "find out what the users want and do the opposite."
"Facilitating the unrestricted use of extensions and themes by end users seems contrary to the central tenets of the GNOME 3 design."
It is not, sometimes GNOME devs even say outright that the project is for their peers and those who share their vision. They do their testing on other GNOME aficionados. In the days of Unity, Canonical did some of their user testing on regular people, those days are long gone.
It truly needs its own fractal of bad design essay save it would have to a farce in 7 parts.
To say that they targeted a different kind of user is insufficiently descriptive. 3.0 was the beginning of ticking off the users they actually had in order to target users they wish they could get with a total package that such users could never encounter in a million years because joe average wasn't installing Linux in 2011 regardless of how simple you made the interface.
9 years later the Linux user base is virtually unchanged and gnome 3 is no longer horrifying as 9 years of labor have rendered it modestly acceptable after the worst ideas were put off or mitigated.
If you spent 300k building a hovel where the roof fell in quarterly and you after much consternation and a decade of work figured out how to keep the roof mostly in place most of the time I would pretty much expect such a project to be the go to horror story among home builders in the neighborhood.
This isn't meanness its just honesty.
I don't ever remember cursing my Windows 3.11 machine that the scrollbar and toolbar icons were distracting in File Manager, nor do I crash my car when the speedometer changes and wish that the distraction of the speedo and rev counter was removed.
I remember using GNOME2 and loving it.
I often wonder constitutes a "power user" - someone who wants to actually get stuff done and not fight the UI to discover things??
I wonder when iOS became the ideal - blindly fumble around whitespace to see if some text is actually a button or if there is some unfathomable control hidden that you need a magic incantation to discover (swipe left on a list control is delete - my mum still doesn't know this)?
Is a "power user" someone who has learned all the different ways of interacting with a modern user interface? You used to learn: click, double-click and scrollwheel. Now every interaction with a control is different and impossible to learn or discover simply by using it. Absymal.
Gnome more or less optimizes for minimal configurability, the theory being that most users want the UI to be as clean as possible. They do not particularly care if someone would like to be able to change some annoying behavior, because they thought that behavior made sense and they feel the cost of adding a button to disable it, or even burying a configuration bit in gconf, is far too high. Of course, they do not have the resources needed to run actual user studies the way Apple, Google, and Microsoft do, so their idea of what users want is mostly based on their own ideas about what users want (since they usually dismiss feature requests from their actual users, because those are "power users").
"There was only one catch and that was Catch-22, which specified that a concern for one’s own UI in the face of flaws that were real and immediate was the process of a power user. Orr was an average user and could be listened to. All he had to do was write a feature request; and as soon as he did, he would no longer be an average user and would have to be ignored."
Also it doesn't even show hibernate button on the "start menu" (or whatever it's called these days) - because apparently the ability to actually power down the box while keeping all states is too confusing to have!