On Gnome, the Super (Windows) key does an Expose (show windows reduced-size and non-overlapping) and lets you launch applications (and more).
On KDE 5, the Super key brings up the Application Launcher, which is nice. And Super+W (which isn't too painful to type) does an Expose. But it would be nice if there was an option for Super to do an Expose and bring up Application Launcher.
Yeah, the Gnome Super key hit the sweat spot for me too. As you say, all the things you wanted the desktop to do are available from that one easy to reach button - swapping between windows, pick something from the launcher menu and text search the applications. KDE has so many configuration options it can emulate just about everything Gnome does - but it can't mimic that exactly.
Gnome (and systemd) seems to want to emulate macOS mostly, and as user of macOS I'm not sure why you would want to do that. But macOS has nothing that matches Super key exactly - so well done to Gnome for that innovation.
That button makes me consider whether my sway setup is worth it, as sometimes I think Gnome can achieve something similar. And even with less cognitive load, sometimes!
The "Overview" effect does all that. Switch window, switch desktop, launch apps, drag windows to different desktops and monitors, etc. In KDE5 it appears to be in the list under Workspace→Workspace Behavior→Desktop Effects→Window Management. …I think I may have had to edit `kwinrc` to get it to bind to just Meta without another key, though:
1. You can go to System Settings -> Keyboard and there, enable Super key to act as another button.
2. Set the shortcut to that another button.