Best Camino to do in July?

Option B will likely be warmer than option A.

The Camino del Norte passes through tons of coastal towns and coastal towns get busy in summer.

An alternative to the Camino del Norte would be Camino Olvidado plus Camino de Invierno plus the last part of the Sanabrés.

In reply to your Norte concerns

1) Yes, but some areas have less, ( Basque country to Markina)and some areas have more asphalt( Santander to Santillana del Mar) so with a bit of investigation you can either jump the sections or find other ways that are maybe longer but cut out some of it.
2) The towns have a historical connection to the Camino through churches, monuments but you have to look harder than the Frances. My experience of the Camino feel is that Albergues play a big factor in this, people meeting up at the end of the day, shared experiences, friendships, The Norte has had many new Albergues open in the last 2-3 years, a few are donativo so the Camino spirit is being promoted.

3) The scenery does change quite dramatically, but differently from the Frances. There is some things that you cannot expect to replicate on the Norte.

The Frances has a lot going for it, but if you walk the Norte without comparing it, then you could have a different but special time.