Both Panasonic GH5S and Olympus E-420 have Four Thirds sized 10.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Another difference between these two cameras is that Panasonic GH5S's sensor lacks 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 GH5S and E-420 sensor size comparison.
Sensor Size and Resolution Comparison image of Panasonic GH5S and Olympus E-420 Cameras
Panasonic GH5S and Olympus E-420 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
Panasonic GH5S
or the
Olympus E-420 ,
including hyperfocal distance.
