I don’t disagree with a lot of what you said, but the applications that use the ribbon are just complex applications with too many commands and options, and while some commands are very common most of them end up having tons of middling use, where it is annoying to have to find them in a menu every time. I think the problem it’s trying to solve is a hard problem and all the other attempts at solving it have a lot of problems too, and I really don’t think menu based design is an improvement. I’m not saying ribbons are the perfect solution, just that the other solutions suck more.
Designed properly the ribbon should take advantage of repeat contexts, so if you’re doing one kind of task repeatedly, it’s likely you need commands from one tab over and over again which beats having to navigate through a menu multiple times. Of course it’s not always designed properly.
Frankly, menu navigation is probably the worst navigation ever devised in terms of hit targets and findability. It has the same organization hurdles of the ribbon, but worse navigation and sometimes nested menus which make things even harder to find. Really, all the ribbon is, is a tab bar on a tool bar, and power users can easily switch tabs with the number hotkeys. The power user option for menus is letter and arrow keys which suck.
Personally, I think the best option for productivity is the command pallet approach like in code editors, but the downside of that is that you need to be a power user to be effective at it.