Gregory Williams gets it.
He's criticising a OS News article called The Problem with Global Menu Bars.
As a past Amiga user I agree with almost everything he says.
The global menu bar is to me still a much more elegant solution than MDI to presenting a proper menu bar, and aids in saving screen real estate (something which was essential back when 640x512, or 640x400 for poor NTSC users, was the resolution of choice).
It gives predictability, and made for a very lean interface.
As for saying "global" menus don't work well with multiple monitors, I don't agree. One of the key features of the Amiga was multiple draggable virtual screens. From that perspective, multiple monitors means just adding more "screens", and the menus were tied to the top of the currently active screen.
I don't even think that the criticism is even based on a power users perspective - I liked the Amiga (and by extension the Mac) approach exactly because it freed up real estate that let me pack a lot more information onto the screen.
The point that there is a key difference between the application oriented approach of Windows and the document oriented approach of the Mac (and to an extent the Amiga) is good, though. The lack of Windows style MDI makes applications a lot more "invisible", and the global menu reinforces that by integrating the application into the overall UI.
This is one of many Amiga features I still miss on my current Linux setup.