I think two meaning of shared path are being confused:
- Shared use as in he wikipedia article linked above, which is reglemened, usually signed, made so it is easy to bike on, usually is in urban settings (or possibly connecting setlements) etc. and in OSM it might be mapped as path or not, but definitely is not what most highway=paths are.
- Shared use as in “access is no specifically designated by anything, so pretty much anything is legaly able to use it (as long as it is not a car)”. This is indeed the only thing that highway=paths have in common, making the tag very vague in its meaning.