Both Fujifilm X-E2S and Panasonic GM5 have 16.0 MP resolution sensors but Fujifilm X-E2S's sensor is APS-C (23.6 x 15.6 mm ) and Panasonic GM5's sensor is Four Thirds (17.3 x 13 mm ).
Since Fujifilm X-E2S'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 Panasonic GM5.
Another difference between these two cameras is that Fujifilm X-E2S'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 X-E2S and GM5 sensor size comparison.
As seen above, Fujifilm X-E2S has a 1.6x Larger sensor area than Panasonic GM5. 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.