In my earlier days, I spent a lot of time working with Koni-Omegas and Graflex XL's, both are more or less similar to Mamiya 23's, holding the camera on it's side for portrait orientation isn't a big deal. Though, all of those "press" style 6x7's benefit from the side grips that are common on them. I'd say the biggest issue for vertical orientation is that the rangefinder spot moves up and down with the camera vertical, but there are always times a split-image focus aid isn't ideally aligned for the subject, and you have to rotate the camera until it is, then move back to whatever orientation you want for the pic.
FWIW, From that time, when I was shooting every day, all day, I also worked a lot with a Rolleiflex TLR, of the three, I liked the Rollei best. Because of size, weight, the camera's orientation never needed to change, and overall handling versatility. I didn't have a prism on the ones I used, but they are an improvement though.