Ubuntu Unity still works. It's basically the Mac desktop but better.
You can get even better space efficiency with a tiling WM. A lot of them don't bother with window chrome or even have a status bar with a clock out of the box.
> You can get even better space efficiency with a tiling WM.
If you try to run the numbers on e.g. sway/i3, that barely makes a dent. Realistically, you can squeeze maybe 6-8px out of a sane window decoration before it gets impractical.
Meanwhile you can get like 10px of vertical space just by halving the vertical padding of a default Adwaita/Breeze button, and it's still larger than the equivalent macOS button which non-technical users can click just fine. Sane sizing on three stacked widgets saves more space than any tiling WM.
We can have nice things without going back to 1980s UI paradigms.
Then just don't use Adwaita/Breeze themes if that bothers you so much? And yes, it's tied to the theme. Ubuntu Unity's default "Ambiance" theme uses much less space. XFCE's default theme also uses less space. You can get themes like Chicago 95 for XFCE which also use less space.
Having visited the third circle of hell before, and having actually gone as far as writing my own theme before giving up the whole charade, I would rather avoid revisiting the fourth circle of hell that GTK theming is.
Edit: also, both Greybird and Ambiance are both really large compared to anything you get on other platforms. It's through no fault of their authors, GTK's layout rules break (or at least broke, I was on GTK 3.24 last I tried it) at low padding values, and it's extremely hard to keep alignment afloat on small widgets. I'm also not exactly young anymore, the text contrast in Greybird's unfocused windows is pretty awful, and fixing anything related to GTK's :backdrop attribute is a very long-winded affair.
You can get even better space efficiency with a tiling WM. A lot of them don't bother with window chrome or even have a status bar with a clock out of the box.