For me a "real" via ferrata isn't a path, so SAC scale have no meaning and probably surface=ground isn't very pertinent.

But… it seem that some contributors use both sac_scale and via_ferrata_scale according to the wiki and/or this long discussion.

https://wiki.openstreetmap.org/wiki/Key:via%20ferrata%20scale

https://community.openstreetmap.org/t/distinguish-via-ferrata-as-sport-build-just-for-the-sake-of-them-from-via-ferratas-that-are-parts-of/120286/19

