But back to my original point, aren't the Phase One corrections just set to apply a certain value to the (generic) distortion slider?
No, for example as you know the HC 35mm has a moustache-like distortion and you cannot fix it with a pincushion slider.
Likewise for falloff as it varies depending on aperture.
If you try Capture One 7 you will see that it now has lens profiles for many DSLR and smaller format lenses including zooms and those profiles deal with distortion, falloff, CA and fringing.
Yair