Both Sony A9 II and Panasonic S1 II have Full frame sized 24.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
One other difference between these two cameras that is worth mentioning is that Panasonic S1 II's sensor doesn't have an anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the A9 Mark II and S1 II sensor size comparison.
Sensor Size and Resolution Comparison image of Sony A9 II and Panasonic S1 II Cameras
Sony A9 II and Panasonic S1 II have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Sony A9 II
or the
Panasonic S1 II ,
including hyperfocal distance.
