IMHO, a medium format SLR is a medium format SLR. Minor differences in features may distinguish one model from another, so one needs to be very specific in comparing any two. For example, it would be fair to compare Bronica ETRSi with Mamiya 645 Pro, but unfair to compare a Mamiya 1000 to Pentax 645, just because of years of feature additions and improvements in the newer cameras.
There is one thing that I greatly dislike specifically about the Pentax 645...the integrated grip is attached at the BACK EDGE of the body, putting all of the weight of the front of the body and lens putting torgue on the hand and no couterbalance! The Mamiya and the Bronica at least have the benefit of using the rear of the body as a counterweight because the (optional) grip is more forward on the body. I have handled all three (as well as Hassy) and ultimately the grip position on the Pentax was considered by me to be a signficant shortcoming of the design. I've never handled a Rollei, but it was always unaffordable, which is why I did not consider it 25 years ago.