Is your '75 on a Rolleiflex? It was, in its day, regarded as the ideal glass for general work, including portraits. The square negatives made cropping to portrait size easy in the darkroom, and all the actual photography required was a small mindset-adjustment to 'visualise' what the finished product would look like as a vertical print.
As a teen I had a small home studio in my Canadian town and I did many portraits. Some were good enough for the municipality to put up a display of my framed work - official snaps of the then mayor and aldermen and some of the town's notable like the police and fire department chiefs - in the main foyer of the town hall. My greatest achievement as a local photographer.
For my work I had a Yashica D TLR on a tripod with two photoflood lights and a small spot as either the background or back of head illumination. My usual go t film was initially 120 Kodak Verichrome Pan, later Ansco/GAF Versapan. Now and then for on-site work I had a Yashica A (the Yashikor lens was distinctly meh!) or a borrowed Super Ikonta 6x6 with a Tessar 80/2.8. No other lenses. Those '80s did all the work.
In 2010 I donated all my 1960s negatives to the town. On checking them I found they were all sharp with good mid-tones, given the high silver content films of that long ago era but also to the 75mm lens. Some were scanned and are now featured on that town's we site, which flatters me no end.
All this to say, in the right hands one lens can do just about everything.
