For many years now KDE has focused on polish, bug fixing and "nice-to-have" improvements rather than major redesigns, and it paid off.
I often wondered why desktop UIs became so terrible somewhere in the 2010s and I don't want to attribute it to laziness, greed, etc... People have been lazy and greedy since people existed, there must have been something else. And I think that mobile is the answer.
UI designers are facing a really hard problem, if not impossible. Most apps nowadays have desktop and mobile variants, and you want some consistency, as you don't want users to relearn everything when switching variants. But mobile platforms, with their small touchscreens are completely different from desktop platforms with their large screens, keyboards and mice. So what do you do?
In addition to mobile, you often need to target the browser too, so: native desktop, native mobile, browser desktop, browser mobile. And then you add commercial consideration like cost, brand identity, and the idea that if you didn't change the UI, you didn't change anything. Commercial considerations have always been a thing, but the multiplication of platforms made it worse, prompting for the idea of running everything in a browser, and having the desktop inferface just being the mobile interface with extra stuff.
You keep the UIs separate. Dumbing down desktop UIs to mobile capabilities is just as bad of a design as it was when people tried to jam a desktop UI into mobile. You have to play to the strengths of the platform you are on, not limit each one based on the other. Yes, it's more work, but it's well worth it to have a product which is actually good.
Linux window managers are mostly made by volunteers, so I’m not picky at all. But, locking the dock and taskbar in place, if anything, seems like extra work. Why would anybody do extra work to make their window manager worse?
You have to install an extension to get a dock at all.
No, there's an auto-hiding dock built-in. Pressing the Super key acts like better version of Apple's Expose feature: it shows the windows you have open, auto-opens the dock, and focuses the application launcher search bar so you can just start typing and launch an app.
You had to install a system tray extension
I'm sure you needed to at some point, but (as you mention), that's no longer the case: it's built in by default.
clipboard manager
If you mean clipboard history... That's true. Although macOS doesn't have a built-in clipboard history viewer either, and I never particularly missed having one. There are plenty of GNOME extensions with clipboard history if you want one.
Generally speaking I like GNOME much more than KDE, since GNOME's gesture support is much better than KDE's. I also personally dislike Windows-style infinitely-nesting-menu taskbars, which is what KDE uses, whereas GNOME is more macOS-like (although it has its own, IMO slightly cleaner style... And of course, it's much more modifiable than macOS).
So, not a Dock.
People don't want their whole desktop to fly everywhere and zoom out when they just want to quickly switch or launch an application with the mouse. They just want to mouse over the bottom of their screen and click.
Same for launching an application via keyboard / doing a calculation / finding an emoji. People just want something akin to Spotlight (think uLauncher on Linux). Something lightweight that pops over and allows them to quickly do the thing, without a lot of visual clutter happening and then happening again in reverse.
for switching between programs, gnome is designed around workspaces instead of stacking and covering windows so you aren't expected to fly into the expose view to switch apps you just swipe to the side to your other program (or scroll in the corner with the mouse, or press meta+alt+left or right).
For launching programs just press meta and type the first couple letters of it's name. This is exactly the same how I open software on windows, and imo it's quicker due to not taking my hands off the keyboard.
I think it's silly to look at a new desktop and be mad at it for not behaving exactly like other desktops. If you grew up using computers that behaved like gnome you'd likely be just as uncomfortable with a stacking based desktop like windows.
I don't want to do that! And, I am in fact a person. I do not want to switch applications by clicking on things with my mouse at the bottom of the screen. I want to switch applications with keyboard shortcuts or with touch gestures, which GNOME has great support for; and both of those can open the dock too (although you can also alt-tab and skip the Expose-style feature).
Again, it's just a matter of preference and taste. My taste is much more strongly in GNOME's default direction than KDE's default direction.