The global menu bar is a design flaw and evolutionary dead end. It doesn't respect Fitt's law when people have multiple monitors. It also implies alt-tab to switch application Vs alt-tab to switch window which is, again, broken when you have multiple monitors (alt-tab to switch window is the correct choice).
Not only that but Fitt's law is dying as mice become less and less used as a means to interact with a device. Touchpads and touchscreens have usurped them.
Fitts's Law is still alive and kicking in the touchpad era. Until we have anything that drives a cursor, it is relevant. A global menu bar is infinitely tall on a touchpad as well because I can randomly flick my finger up and I will have reached it.
And I do not get what a global menu bar has to do with window switching and monitor switching. Tiling WM fans all know that focus-follows-mouse is saner than alt-tabbing like a maniac, and this doesn't invalidate the role of a global menu-bar.
Not only that but Fitt's law is dying as mice become less and less used as a means to interact with a device. Touchpads and touchscreens have usurped them.