Just to add our two-penny-worth, and probably more to illustrate that each individual will have an individual answer to this question:
we were walking part of the Norte in April this year. After asking this very same question we took the 40-year-old down sleeping bags, and Peter took a fleece liner (in old-fashioned camping parlance we call these 'sheet sleeping bags') because he feels the cold easily and Bridget took a home-made polycotton one, because I am a woman of a 'certain age' and seem to keep warmer than him. We found that there were blankets in the first few albergues we slept in, so we only needed the liners. And I found the down sleeping bag too warm in crowded rooms with no window open, so I just used it like a throw to pull over cool patches if I needed to.
So we left the sleeping bags behind in a hotel in Santander to be collected on our return journey, to reduce weight, together with such luxuries as the second pair of trousers!
Lo and behold, we came to an albergue where the rule was 'no blankets' because of bugs. Two were kindly lent to us though, but rather thin ones. Peter had to wear all his clothes. We survived!
This is an impossible question!
We are going to ask for very light modern sleeping bags for Christmas! But I would still want a thin liner as well a) for washing and b) for those warm nights when you want lightness with decency!
best to be prepared for less than perfection sometimes, and make the best of whatever you have!