Sony RX1 has a 24.0MP Full frame (35.8 x 23.8 mm ) sized CMOS sensor . On the other hand, Sony A7S II has a 12.0MP Full frame (35.6 x 23.8 mm ) sized CMOS sensor and features Bionz X processor. Sony RX1's sensor provides 12MP more than Sony A7S II's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the RX1 and A7S II sensor size comparison.
Sony RX1 and Sony A7S II have almost the same sensor size so none of them has any significant advantage over other in this area.