Both Fujifilm X-Pro2 and Leica SL have 24.0 MP resolution sensors but Fujifilm X-Pro2's sensor is APS-C (23.6 x 15.6 mm ) and Leica SL's sensor is Full frame (36 x 24 mm ).
Since Leica SL'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 X-Pro2.
Another similarity between these two cameras is that both Leica SL and Fujifilm X-Pro2 sensors lack anti-alias (Low-Pass) filters. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moire occurring in certain scenes.
Below you can see the X-Pro2 and SL sensor size comparison.
As seen above, Leica SL has a 2.3x Larger sensor area than Fujifilm X-Pro2. 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.