>Any argument against global menus are really unfounded

I disagree, for an example: global menus do not work well at all with focus-follows-mouse. It's not really possible to design a good system that has both. I've seen various attempts to try to make focus-follows-mouse work on macOS, and the usability is very poor. Similarly, you will have bad usability trying to plug global menus into a system that isn't really focused around the concept of menus.

But I think you're right that in the end it doesn't really matter, someone can get used to doing it either way.