Aren't there many places where a highway with no sidewalk is the only walkable option? So if someone saw your not-walkable, they might think not walkable at all.
Seems like you guys had two different perspectives, both arguably right. Maybe it needs to be split into technically-walkable and comfortably-walkable layers.
The trouble is you start getting into subjectivity. Some people are comfortable with vie ferrate, many are not. The only thing you can do is tag with objective features that can be verified on the ground, including physical features and legal restrictions that are indicated by signage.
Or add a "probability of injury or death" attribute for more granularity.