What are the "overshift" situations? Overshifts from what I'm imagining are incorrect adjustment of the limit screws. Of course improper mounting of the cable to the hold down and adjusting the inline cable adjustments for the wrong reason will add to the mess of figuring out what is really wrong.
I've got a 105 5801 that will be going on my other bike soon. Maybe I'll see what you think is so wrong with the 5800 then. But for now all I can see is perhaps the 5800 front DR is a design that allows too many way to install it wrong or adjust it wrong. . But for me, the 5800 FD has been as good as any other I've had.