So if we discuss the generic vs. intuitive path separately, I think that there already are sufficient tags to describe the difficulty of an actual path/trail:
hw=: This is a well-made, wide, often paved way with no difficulty, usually easily passable even for wheelchairs. You can always expect that it is easy to use for the designated mode of travel.
hw=<whatever resembles a real hiking trail, possibly single-track>: This should be combined with the well-established sac_scale to describe difficulty for hikers, (or mtb for bikes or horse_scale for riders). Without further tagging it should imply sac_scale=hiking
hw=via_ferrata: Real climbing paths, only for climbers
I think sac_scale already covers the whole range of hiking trails:
sac_scale=hikingis already defined for simple, no-care trails. Wiki says: “Requirements: None. Can be hiked in ordinary sports shoes/trainers. Orientation straightforward, even without a map”sac_scale=demanding_alpine_hiking/difficult_alpine_hikingalready cover simple and challenging stretches with climbing and mountaineering equipment
Therefore I see no need for extra tagging for climbing or scrambling, that is already included in sac_scale.
Beyond that, I agree that legal access and usability should be strictly separated, and usability must be separated by mode of use (sac_scale, mtb:, horse_scale) to make sense and not mixed up/implying a specific mode (smoothness). Again, the dilemma is that path is a misleading tag resulting in ambiguous use, so we need to evaluate the access tags to try and guess what it actually means. But that’s the other topic again. 