I'm not talking about fitts law on phones though, I don't think anyone is. This is about Tahoe/mac OS on Macs.
But I'd hardly call a mouse, or a trackpad 'increasingly obscure' I use the fact that I have an infinite target area with my trackpad everyday. It's one of those things that a user might not consciously notice until it's no longer there. Much like a lot of what we are seeing with Tahoe in general that people like me, you, the author of this article. We are pointing out the UI issues that are suddenly immediately apparent, and the bit that is really astounding us all is --- how on earth are Apple, supposed bastions of UI interface detail, and polish , are making such an almighty meal of all of these things that used to work but now just don't, and not even don't work -- the 'new ways' are objectively worse.
The only criticism of the top menu bar interface is that on big hi res monitors (which are relatively recent in terms of the Mac OS desktop) sometimes have the menu bar 'miles away' from the actual app that may be in a smaller window. But this is where fitts law comes in -- so the choice is shorter distance but you need to be more precise smaller target (windows) or large distance but infinite target. I prefer the latter.
It's probably in some ways almost a direct holdover from the time of 9" screens and single tasking -- apps were usually taking up most of the screen so having a menu bar at the 'top' wasn't that weird. Having multiple menus bars would have been really weird and taken a lot of space.
I mean Apple could offer an option like I used to see on gnome where you could have a global menu bar or a per app menu bar. That would be more useful than stage manager ever has been I'd bet.