How so? Double-clicking an AppImage from a specific folder is not user-hostile (that's a common pattern across desktop systems), and the blogpost specifically points to appimaged and AppImageLauncher as solutions for full desktop integration.

Desktops integrate poorly with desktops.

What do you mean? When I think of "...integrate poorly with desktops", I think of Electron apps. These also have a Flatpak-like distribution (but not security) model. And a "best effort" integration model. Basically, whatever is possible without lifting too much of a finger.

When i think of "desktop integration", i think about drag and drop not working between `ark` (a QT program) and `thunar` (a GTK program), and i think of folk writing blog posts about window theming. (there's also notifications, icons, etc, blablabla, that keeps getting worse (freedesktop is, that is))

To be honest, i don't care much about how programs look. But i do know many people do care.