Sigma DP2 Quattro has a
20.0MP APS-C (23.5 x 15.7 mm ) sized CMOS (Foveon X3) sensor and features TRUE III engine processor. On the other hand, Fujifilm X100VI has a
40.0MP APS-C (23.5 x 15.6 mm ) sized BSI-CMOS sensor and features X-Processor 5 processor.
Fujifilm X100VI's sensor provides 20MP more than Sigma DP2 Quattro's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
One other difference between these two cameras that is worth mentioning is that Fujifilm X100VI's sensor doesn't have an 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 DP2 Quattro and X100VI sensor size comparison.
Sensor Size and Resolution Comparison image of Sigma DP2 Quattro and Fujifilm X100VI Cameras
Sigma DP2 Quattro and Fujifilm X100VI have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Sigma DP2 Quattro
or the
Fujifilm X100VI ,
including hyperfocal distance.