Honestly I just want KDE to do the backbone and GNOME to do the designs.

Adwaita apps look just right, minimalistic yet powerful, pinnacle of modern simplified designs. Everything you actually need is close, and the rest doesn't clog the view.

The rest of GNOME is heavily meh. Customization is next to nothing, and generally any workflow falling outside the one window = one task paradigm is gonna be a pain. Settings are convoluted and sometimes straight up unreachable without additional tools or config edits (and sometimes they don't even apply).

I guess what unites Adwaita and GNOME project overall is the stubborn adversity to users making it comfy for themselves - it's the GNOME way, or no way. And while Adwaita is at least actually good in its defaults, GNOME is not.

KDE, on the other hand, is brilliant as a desktop environment, but menus could be so, so much better. So, when I have a choice, I use Adwaita-themed apps on KDE. With proper theming on KDE side of things, they come together just right.