Both Olympus E-PL9 and Fujifilm X-T10 have 16.0 MP resolution sensors but Olympus E-PL9's sensor is Four Thirds (17.3 x 13 mm ) and Fujifilm X-T10's sensor is APS-C (23.6 x 15.6 mm ).
Since Fujifilm X-T10'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 Olympus E-PL9.
Below you can see the E-PL9 and X-T10 sensor size comparison.
As seen above, Fujifilm X-T10 has a 1.6x Larger sensor area than Olympus E-PL9. 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.