Okay, maybe I should have added some guillemets to «harmoniser». 
What I worry about is this setting a precedent, whereby reclassifying this road snowballs into unnecessarily or inappropriately reclassifying roads all over the damn place.
And maybe I should restate: I think it already is “harmonized”. It’s tagged with highway=primary because it is a more important connection than secondary, but not as important as trunk. It seems perfectly reasonable to me the way it is.