I get the feeling that we agree that a highway=path can vary widely in access and in physical characteristics.
If access and physical characteristics are tagged on the feature, data consumers can use the extra tags for their target groups and applications, such as maps and routing profiles.
If they don’t, they are not optimally serving their users.
For highway=path without any other tags, data consumers who do use the differentiating tags, will have to decide on default values for those tags.
The access tags are easy: world wide defaults are: general access=no, foot=yes, bicycle=yes, horse=yes. I would add: oneway=no.
What, if any, are sensible world wide defaults for width, height, visibility, incline/decline, smoothness, surface, various skill scales et cetera?
e.g. Could a minimum width of 50 cm and a maximum width of 200 cm be assumed, with a tendency toward the narrow end, meaning that in the absence of any width tag, a path could be rendered as 1.5 m wide, which physically allows foot, bicycle, and horse access.