Splitting hairs. 75mm fills the same niche as 80mm, more or less.
A 50mm + 75mm pair is, together, enough different from a 50mm + 80mm pair that it is worth paying attention to.
In my case, I consider a 55mm lens as essentially my standard lens, with a 45mm being a wide lens.
The 80mm or 110mm fulfil my needs for something slightly longer.
I used to work printing proofs and machine enlargements for professional photographers who mainly did wedding and portrait work. The 6x4.5 negatives came from Bronica camera, Mamiya cameras and (I think) Hasselblad cameras. I saw a lot of negatives, and made a lot of prints, and unless I happened to know which cameras were being used, I wouldn't usually have been able to tell.
Some of those negatives ended up as large custom prints - again the quality and characteristics of the camera and lens systems didn't seem to determine the quality of the results.
Around the same time, I sold Mamiya and Hasselblad cameras and lenses - although not Bronica. My experience handling (but not using myself) Bronica 6x4.5 equipment is more recent. The ergonomics and approach to things like filter use are really different between all three. The difference between leaf shutters and focal plane shutters is important too. Close focusing capability can be important as well.
I like my Mamiya 645 Pro and the raft of lenses and accessories. The following comments relate to this.
The system suits my left-handed needs. The lenses are consistent in colour rendition and quality, with excellent resolution and contrast. For most of the lenses, the focus throw is short and the close focusing capabilities permit close framing. 55mm is the standard filter size for a number of the lenses, and 67mm is standard for the 45mm and 80mm macro (the 80mm standard also uses 55mm filters).
All of the lenses have excellent focusing grips, and all the lenses that use 55mm filters can be used with the excellent, detachable focus assist lever.
The aperture rings on all my lenses offer clear, easy to read numbers and positive click stops - in some cases half stops.
The 55mm lens is relatively tiny. I have the relatively rare waist level finder for my camera, so as long as I'm comfortable with landscape orientation only, I can go out with the 55mm lens and WLF on and the combination is wonderfully light and compact - great for something like the local on the street annual classic car show. The 80mm standard lens isn't a lot bigger than the 55mm lens.
This example is one of the 55mm at the car show examples, resized down for the old Photrio requirements: