Both Fujifilm S1 and Panasonic GX85 have 16.0 MP resolution sensors but Fujifilm S1's sensor is 1/2.3" (6.17 x 4.55 mm ) and Panasonic GX85's sensor is Four Thirds (17.3 x 13 mm ).
Since Panasonic GX85's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Fujifilm S1.
Below you can see the S1 and GX85 sensor size comparison.
As seen above, Panasonic GX85 has a 8.0x Larger sensor area than Fujifilm S1. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.