Both Olympus TG-870 and Panasonic TS6 have 16.0 MP resolution sensors but Olympus TG-870's sensor is 1/2.3" (6.17 x 4.55 mm ) and Panasonic TS6's sensor is 1/2.33" (6.08 x 4.56 mm ).
Since Olympus TG-870'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 TS6.
Below you can see the TG-870 and TS6 sensor size comparison.
Olympus TG-870 and Panasonic TS6 have almost the same sensor size so none of them has any significant advantage over other in providing control over depth of field when used with same focal length and aperture.