> Mac's UI is optimized around the assumption most users won't expand windows to fill the whole screen, but rather leave them half-sized somewhere in the middle

The assumption is that the window should be the size of the content of the document inside.

It turns out that this approach works well for many applications, especially what the mac was designed for in the 80s and 90s. And it's horrid for modern "pro" applications.

Bring back the floating toolbars of the early 2000's and it'd be fine.