After looking at the trailblazed:visibility page (which is a lot clearer wording in my opinion), the iD editor, and comments here I’d propose these for new visibility descriptions:
trail_visibility=excellent
Unambiguous well-constructed path everywhere. Easily followable when visibility is reduced.
None, orientation unproblematic, no map required
trail_visibility=good
A continuous path which is always visible but occasionally may have to be searched for.
Basic sense of direction, map recommended
trail_visibility=intermediate
Path mostly easily visible, but has short sections where it is hard to find.
Good sense of direction, map required
trail_visibility=bad
A path mostly exists, but the mapped way is partly pathless and you need to be able to find the path again.
Basic skills in orientation
trail_visibility=horrible
Often or mostly pathless, signs of a path exist but are often rare or hard to locate.
Advanced orientational skills
trail_visibility=no
Pathless (should be used for short segments between paths to help with routing).
Excellent orientational skills
The bright line around intermediate seems to be the hardest to define, I tried not to change the line too much, but I feel like this has more clarity to it. No is my opinion, and refers to pathless paths / routes which has it’s own topic.
The text in the iD editor needs some tweaking too, Bad doesn’t necessarily mean no markers.
There’s also the contradiction on whether this includes markers or not on the talk page, I also condensed down ground vs landscape wording, fixed references to “routing” etc for the text up top.