Completely agree. I use Rectangle, largely for the most basic thing that MacOS gets wrong: maximizing windows. It shouldn't be the same as "full screen". I know that you can double tap a window's top bar to maximize, but this should be swapped with the full-screen toggle. And cmd+shift+f should maximize the window instead of going to full-screen.
I feel I've regained some sanity with https://github.com/koekeishiya/yabai - even without messing with System Integrity Protection. It's a shame there's no real Api to enable proper screen/desktop/wm on macos though.
