Team Phase One users are very enthusiastic about using C1 with Team Phase One backs. The saying is that maker's software should always be used for best results.
AFAIK, Capture One doesn't support non Team Phase One MFD. Hasselblad users have Phocus which is tuned to Hasselblad backs. But, as far as I know neither Pentax nor Leica have their own raw workflow software for the cameras. Still it seems that both Leica and Pentax users are very satisfied with their systems. So what software do they use?
A partial explanation may be that both Pentax and Leica embed camera specific DNG Colour Profiles in their DNG images that may be superior to the ones delivered by Adobe.
Would be interesting to hear something about raw conversion on non Phase One backs.
I know about a couple guys who use or used to use RawTherapee.