Both Fujifilm S5 Pro and Fujifilm S2 Pro have 6.0 MP resolution sensors but Fujifilm S5 Pro's sensor is APS-C (23 x 15.5 mm ) and Fujifilm S2 Pro's sensor is APS-C (23 x 15.5 mm ).
Since Fujifilm S2 Pro'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 S5 Pro.
Below you can see the S5 Pro and S2 Pro sensor size comparison.
Fujifilm S5 Pro and Fujifilm S2 Pro 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.