I agree, and think that this describes the problem very well. Right now we have one tag value trying to store two pieces of information - “what is the legal right of access of traffic mode X” and “was this highway=whatever designed for the use of traffic mode X”.
The one absolutely does not imply the other (even before considering “esoteric” modes such as snowmobile). I can think of plenty of places locally (in England) where there is a legal right of bicycle access but it was never designed for and is completely unsuitable for that mode, and plenty of places designed for bicycle (or horse) use where the legal access is only “permissive” - permission can be removed at any time.