You keep repeating this point, and insisting that there isn’t a relevant distinction to be made with legal access and physical suitability, and that they are equally self-explanatory. I’d argue that this is a classic case of a category mistake. Like saying that colours have a smell. Signage and laws are explicit. Suitability is not only subjective, but also multi-modal by nature.
Put explicitly another way: would you think it fine to tag a way with both bicycle=no and mtb:scale=⟨>1⟩? I’d say it’s a contradictory pair. A mountain bike is a kind of bicycle. If I ever came across a way tagged like that, I’d immediately remove the access tag.
Regarding the Boolean value first-approximation argument: confounding legal access and suitability under the same key, and under the same =no value (as your examples repeatedly show) seems to many of us an absurd proposition. I mean, take a look at the example pictures of ways tagged >1 on the mtb:scale key!
Earlier, you mentioned that you’d be OK with a subkey that “pertains to both permission and reachability.” @julcnx asked you for a concrete example. It’s a long thread and I may have missed that example, but could you point to your answer?