No, I do not think this is wrong.

The French version of MapFeatures (osm.wiki/FR:%C3%89l%C3%A9ments_cartographiques) implies that roads with that sign are tagged with highway=trunk. That is not written explicitely, but the road sign is shown there. Also, osm.wiki/OSM_tags_for_routing/Access-Restrictions#France states that motorway and trunk have the same access restrictions in France. And since motorroad=yes means that motorroad-like access restrictions apply this does not add any information in France and is therefore redundant.

I am all for consistency and for avoiding redundancy. Since I am occasionally do some mapping in France I refer to the wiki when I am not sure about local conventions.

In this case only the northbound part of N57 had motorroad=yes. This was inconsistent. And since hidhway=trunk implies the same restrictions anyway I decided to remove that tag.

While it is not directly harmful to add tags that do not add information I try to avoid those for simplicity.

Yes, someone wrote down his opinion, nobody corrected him and I agree with it. That is enough for me.

osm.wiki/OSM_tags_for_routing/Access-Restrictions#France also shows the same restrictions for trunk and motorway in France. So motorroad is redundant.

After all the whole OSM wiki is just someone's opinion. So one cannot rely on anything that is written there?

Well, I consider this wrong. How do you determine the limits up to which motorway regulations apply? I don't believe this is indicated in France. So it seems like they are tagged as _link up to the first split.

Anyway, I did not realize that this has evolved into standard practice. Since that seems to be widely accepted I will change those back.

The tag was only applied to one direction of a two carriage way.

motorroad=*#France says for France: "This tag is not required, just use highway=trunk."