Before: https://simon.shimmerproject.org/wp-content/uploads/sites/3/...

After: https://simon.shimmerproject.org/wp-content/uploads/sites/3/...

The old title bar plus toolbar combined took up 56 pixels of vertical space. The new version takes up 46 pixels, loses the title display, two of the toolbar buttons, and two of the dropdown arrows. And you're not going to be able to simply turn off the toolbar anymore, like you often could in traditional applications (I often do this in text editors, for instance.)

> Or do I misunderstand that these two things are in fact coupled?

This part is really tricky. GTK3 itself does not mandate CSDs, although it does force them onto all of its common dialogs. Gnome 3 tends to take this to the extreme and is trying to remove any and all title bars from every application of theirs. I can live with my file open/save dialog not having a title bar, but I don't want my main windows to lack them as well =(