In my reading of the Wiki Documentation, a path with markers will always get visibility excellent (markers everywhere) or good (next marker always visible, but sometimes has to be searched for). Only paths without markings can go intermediate or lower. Perhaps, that is why I did not tag visibility, when I added the trailblazing key near Kraspes. Trust me, from cairn to cairn, there is just rocks; Likely, because people just navigate from their personal assessment of the terrain. There are lots of such paths in the so-called nival zone, For the Sherlock Holmes around, they can search for lichen scrubbed, but they will not make miles then. I just cannot map trail_visibilty=good for that.
In the end, maybe the key should more explicitly say: It is about the ease or lack thereof in following the path as mapped in OSM. So to say, the navigational aids presented by not only human feet but also human hands.