Hello
My opinion on the mapping of these "paths" is that while OSM might show a path going across an area of open access, it's not as if people rigidly just stick to exactly the same line on the map. UNLESS the grass is mown to encourage people to only follow that route. Waden Hill in particular to me has quite a wide area of grass that people use.
 I can see that West Kennet Avenue is more of an issue, as the obvious route to walk along is between the lines of stones