Afi/Hy6 is not better for Phase One than Mamiya because it is the wrong format. All current Phase backs are 645 or smaller. The Afi/Hy6 is 6x6 format so they would be only partially compatible. Mamiya was a major player in MF in the era of film, they only made that --and some golf equipment, I think--. They had a 6x7, 6x6 range finder, a 6x6 twin lens reflex with interchangeable lenses, the 6x7 RB, the RZ 67 and a full 645 system. I think they where one of the first with that format. The AFD is probably the longest in production 645 system. In Japan I saw a Hasselblad that had the Fujifilm logo. That is probably why they have been able to survive where the majority of other camera makers have gone under. I have had 4 different Mamiya systems, from twin lens reflex to RZ II and AFD and I have never had one failed to work.
Development in this field is sloooow probably for a reason. It is a very difficult market with an elite user base. There are probably little resources and mistakes can cost the life of the brand. Mamiya almost went down with the ZD camera and back... Hasselblad gambled with the closing of their system and got more time in the game. Afi/Hy6 continue to play and are sitting at the table. We can only wait and see their next move..