There appears to be a residential area darkening going from z13 to z12 such that roads and surrounding areas are very similar in shade but different colour - so the roads don’t stand out as much. Could this be the problem ? Removing residential detail - or lightening it may make the roads clearer - and this would only apply in built-up areas - so affecting them without affecting more rural areas that don’t have much of a problem now.

I think OSM offering different styles (standard, Humanitarian, Transport, Cycle) is a bad idea. I think the Standard map should be all OSM naturally offers. It doesn’t stop others doing their own thing.

I think the standard map should show everything - as otherwise what’s the point of putting something in the database if it’s not going to show on the map ?

I think the standard map should show checkboxes - to be unchecked - grouped as per the tag categories so users can deselect items they don’t want to see on the map. OSM could offer preset checkbox selections for cycle, humanitarian, transport etc.