This argument never made much sense to me, although I do subscribe to Fitts' Law. With desktop monitor sizes since 20+ years ago, the distance you have to travel, together with the visual disconnect between application and the menu bar, negates the easier targetability. And with smaller screen sizes, you would generally maximize the application window anyway, resulting in the same targetability.

The actual historical rationale for the top menu bar was different, as explained by Bill Atkinson in this video: https://news.ycombinator.com/item?id=44338182. The problem was that due to the small screen size, non-maximized windows often weren't wide enough to show all menus, and there often wasn't enough space vertically below the window's menu bar to show all menu items. That's why they moved the menus to the top of the screen, so that there always was enough space, and despite the drawback, as Atkinson notes, of having to move the mouse all the way to the top. This drawback was significant enough that it made them implement mouse pointer acceleration to compensate.

So targetability wasn't the motivation at all, that is a retconned explanation. And the actual motivation doesn't apply anymore on today's large and high-resolution screens.