KDE does have a long tail of (more or less maintained) apps, but there's nothing stopping you from installing the WM and plasmashell alone, along with a small selection of apps like Dolphin and Konsole. (You will spend a lot of disk space on KF5, and you might want to avoid Akonadi-based PIM apps too.) Do you think KWin/plasmashell is bad software (admittedly KWin has bugs, and plasmashell is worse off for being based off QML/JS and using janky drag-drop interfaces instead of traditional widgets), or are you avoiding it just because developers spend effort on apps?

You could try liquidshell as a plasmashell replacement, but I didn't like it (can't right-click to customize the panel, no Windows 7 style taskbar-dock IIRC).

There's Deepin too, but that's developed in China (which might be fine) and comes with a suite of applications (you probably won't like it either). I don't understand why you're fine with GNOME or XFCE though, since they also come with a suite of applications (GNOME has a file manager, text editor, terminal, IDE, browser, and VM GUI, and XFCE has a file manager, text editor, and terminal).