But the other value in Filmic (remember, these are two simplified parameters for convenience of use, full filmic has 5 parameters), "Shadows" is not really contrast, I guess this is something from 'toe' on the curve, it's like Shadows in parametric curve adjustments (for example in CameraRaw). It should prevent the washed-out look.
Contrast on other hand is S-curve (or should be !) which should affect everything ( shadows, darks, lights, highlights). So you can definitely use both at same time, they achieve different things.