I disagree that the tag is clear. The wiki defines the tag in terms of itself. I believe it should be the lack obstructions. An average trail will likely have some tall grass, a few low hang limbs or easily avoidable stones. A great one will be clear enough to run through. bout path clearance not visibility. The surface and smoothness tags can handle whether the ground conditions.
The other part of problem is that the current “visibility” values include aspects of how well a path is marked with signage. The two are different but related attributes of a trail. Signage has really nothing to do with be able to travel the trail itself. They become important when deciding which trail you should be on. The level of quality of marking should be a seperate tag with its own set of values.