From reading the anecdotal reports here on TMC over the years, this seems to be another case in which the first version of AutoPilot was better than the newer cars. As I understand it, the MP1 cars have a separate sensor for rain, whereas the later cars do not (at least on Model S). The auto wiper function is not great on my 2015, but I find it satisfactory. By coincidence, I was on a long drive yesterday that involved intermittent mist, fog, light rain and some heavy downpours, and left them set on one of the auto settings for the entire time. The wiper blades were juddering a bit during the lighter rain, which may mean I need to replace the blades.