AnneDrogyny - I am inclined to agree with you. I do think a number of Devon independent schools are focussing on boarding when really there is a market for day pupils they are not tapping into because they fail to " woo " them in the same way.Often I feel, when visiting schools,that as a day parent I am a tag along. But I have no need for my DC to board and do not want it , aside of the fees. We can though afford day fees - although sometimes those are seemingly steep for what you get. I comparethat as money spent ensuring my DC has an education rather than being put in a large class with a lot of distractions and difficulties to hinder learning.
Also, I think the boarding market is (certainly here in SW) dominated by those groups from overseas you mention and not all are that able. I have a friend whith a DC in boarding in a school in Devon. She is the only one from Britain in boarding (which says something to your point about how many local parents can afford boarding). The others are from around the world. Whilst some arevery bright and able, many get into good universities often on reduced grade offers (British child AAB - overseas, BC and IELTS 6- I have seen this happen at Russel Group universities).
Whilst I think it is good for DC to have an experience of other cultures, I am not sure they need to be put in classes with pupils who have a limited grasp of English. Whilst I do not want to sound rude, that is one thing I am trying to get away from by paying for a school rather than using the local state one.
Whether the other pupils are academic or not is less of an issue to me than whether they are disciplined and well mannered children who work when at school and do not disrupt the learning of others.
I do not think you need to be in a classroom of "clever" children to do well, although I would draw the line at my DC being in a class with children with lots of problems and challenges.
I think independent schools are good at bringing out the best in middle of the road children who might otherwise get lost in an over large system, or DC who are less confident or outgoing. I think with a bright DC, they will most likely do well anywhere.
In addition to the problem you highlight on boarding, a big problem with some of the schools is that they want only the most able ( to bump their figures) and because most parents are so vain they want to say their DC got into this or that top academic school. Looking at such schools it seems tome a Dc is fine as long as they are top of the milk bottle in that school. Other, maybe equally able (in terms of IQ etc) DC will be left to fend for themselves, where in a another school which is less highly selective, DC may find teachers more willing to help them achieve in some area. They may even find an area they can achieve in (which may not be the case when faced with a competitive and highly able group in a very selective school). Effectively many of these independent schools are acting like grammar schools ( and in many parts of Devon we have those for free already).
What I want for my DC is a nice intermediate school - not one who only wants the most able but one who will take the "grammar school failure" who may only have just missed the pass mark rather than the
"nice but dim". What I did not grasp early enough when I came to Devon is that most state schools are not preparing DC for the 11+. It was only when I was sent a list of things that were required learning for the 11+ that I realised the school had not taught them and I have not been quick enough off the mark getting a tutor.
The issue is that being top heavy clever does not make you successful in the world. Most of our DC can achieve what the "very academic" do. It requires a level of intelligence, not necessarily a genious. If you find that hard to accept, just think about it this way,there are a limited number of top positions. Of the others, most end up working with people who have had a variety of university experiences. I work with people from Plymouth and from Oxbridge, we all do the same job. Does that make the Oxbridge people failures or the Plymouth ones successful?
Overall, like you I wish some of the local independents would offer a little more to local parents who want to send their DC to an independent day school. I think there may be a big market out there for a school prepared to focus on local children/parents and offer them the opportunity to get a decent school at a reasonable cost. Rather like those schools my mother was able to go to as a day pupil.
So there we are, I have said my bit. Rather long, I am sorry.