You have a point, I remember starting in St Jean on our first Camino, when researching the route and checking out the height of this pass I remembering thinking " pah they are just hills" I've climbed a number of mountains so wasn't that worried about them, but crawling up and up on that first day I kept wondering "are we there yet" and was glad the cloud cover shrouded the top still hours away. I probably had a lot to do with the weight I carried in my pack. I've learnt a lot since that first Camino and I'll never call the Pyreneese just hills again.
Having complete many other long routes to Santiago, and the sea beyond, while I love the hot dry country (and this is why we go to Spain) coming into the green hills of Galicia is a but like coming home. It's just a bit tiring after walking so far to be back going up and down multiple times a day. So I would never call Galicia flat.