I think you are right about the quality of life in France but perhaps not about Devon & Cornwall.
I owned property in very rural Devon for many years and also lived there permanently for about 7 years. 25 years ago it was lovely and certainly different to the London area. Now it is busy, house prices have rocketed up wards and I fear that the region will have problems soon. For example, my son who lives in North Devon, despite running a successful business, is really struggling to find an affordable home to buy. He is on the point of resigning to the fact that he will not be able to do so, at least for a long time. One reason could be that as London gets more expensive and crowded it expands more and more into the countryside. Also, there are a large number of houses used as holiday homes by wealthy people from London and the Midlands as weekend retreats and the roads are clogged up by their ridiculous BMW X5's, Landcruisers and the like. The scenery is fabulous in the West County but I do feel that so far as the quality of life is concerned it is pretty much the same as the rest of the UK.
I travel to the West Country on business regularly, was there yesterday, and really have noticed huge changes over the last 25 years or so, mostly for the worse which is a real shame.
Life is what you make it, wherever you live.