I happened to use this path last week. It really is a path that is only comfortable on a mountain bike. As I was entering it, people in front of us were making an about-turn because it was too hard for them.
This entire section is affected:
https://www.openstreetmap.org/directions?engine=graphhopper_foot&route=50.39334%2C5.53400%3B50.38132%2C5.52437
All of it has some clarifying tags about path quality, so I'm not sure we should do anything more? Since it is part of the PreRavel network, I guess cycleway isn't that bad?