C1 does not provide a superior conversion of 645z files in any respect. Unless you cannot deal with using LR, there is really no reason to bother. If I chose to shoot with a Phase back, I would be using C1. That's what works best.
Conversely, shooting with the 645z entails using LR. Deal with it or use a different camera. I've always intensely disliked C1, so it makes me disinclined to use Phase gear. Don't waste a lot of mental/creative energy trying to train your cat to be a dog...
I agree with you completely about C1 and its usage.
It has taken me some time to get used to it where I now don't curse at it. Now I just do what I need in it, which is process the files with no layers, no other hoopla. Just expose, color, details structure shadows, lens, all that stuff. I export into my LR catalog, and use the 16bit TIF to do any overlay edits to the file. So i simply use it to capture and process, which I think is the strong point. All else for my needs is "bloatware"(of course thats just my needs :-)
Regardless, I see that it can get finer details from the Phase files. Now that maybe just for PhaseOne MF back files, as that is my experience. It very noticeably better resolves than the LR on Phase files.
Shooting with DSLR, I don't look for this level of critical detail so I stay with LR.