Agreed regarding the variability of soft shell. Some are not breathable at all.
It’s so dependant on how you hot you burn. I wear significantly less than the guys I ride with, I prefer to be cold for the first 10 mins and just right for the rest of the time, they hate the feeling if being cold and open zips etc as the ride goes on.
My recommendation for road riding in the cold ( 0- 3deg c) is textran thermo or something similar – I found a bargain Campag top and Morvelo do a thermoactive top. Both do me on the coldest days with a thin berghaus LS base layer. This fabric seems to have the right combination of keeping warm in but allowing breathability to keep the worst of the damp out.
I don’t think there is a solution for rain. You either get wet from the rain if you’re not wearing a shell or wet from sweat if you’re working at any moderate effort because manufacturers’ claims for breathability may sound wonderful, and event and gore text certainly breath better than other membranes, but I just cook inside.