Had a look at her post, she divides the 75% into 3 sections, 25% on or alongside motorways, 25% on concrete tracks and 25% on quite country lanes. For the motorways I remember about 10km leaving Santander, about 5km before joining the coastal route to Llanes, and about 10km between Gijon and Aviles, push it up to 30km total for very little bits I cant remember, work out the % for yourself out of 820-850km, even the motorway before joining the E9 to Llanes might have another option, I keep seeing photos of places which I do not remember walking and it seems that once you get to the motorway you cross it now and join the coastal path earlier. Coming out of Santander, you can either take a train which misses out the first 18-20km, or go to the coast again and follow it around to Boo which makes a 12km section go up to about 18km, but takes out the asphalt. Gijon to Aviles is bad, character building is the best way to describe it.
I would say about 40% quiet country lanes/roads and cycle paths, around 40% trail which is a mix of proper trail and gravelly farm roads.
I think I know where shes coming from have alook at her list of walks, she has been on some truly natural, wild and remote ones but the camino is a pilgrimage to Santiago, some caminos will tick her boxes of what is a good route and not, the Norte has feet in many camps and over the length of it all added together I feel it shows you many different aspects of Spain and of yourself.
Buen Camino