Both Panasonic S1 and Sony A9 have Full frame sized 24.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Another similarity between these two cameras is that both Sony A9 and Panasonic S1 sensors lack anti-alias (Low-Pass) filters. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moire occurring in certain scenes.
Below you can see the S1 and A9 sensor size comparison.
Panasonic S1 and Sony A9 have sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.