Honestly outside London there are many almost non selective independents. Passing the exam to get in my ds school is pretty straightforward and they have an fairly large SEN dept. An increasing number of parents choose independents precisely because they can cater for individual needs. Of course there are hothouses but there are also lots of mixed ability schools as well.
The most expensive school we paid for was a specialist school for our middle dc who had complex spld, a combination of ADD, dyspraxia and dyscalculia . Our local school said they would put him in the bottom set, they ‘thought it unlikely he would get a C in anything’ could not accommodate his music because ‘ bottom stream don’t do music’ and he would be in a class of 30 . Also said that they weren’t keen on taking people who didn’t come with funding ….nice to feel welcome.
Instead he ended up with several GCSEs at C above including English and maths and music , he played in the orchestra, was scorer for the cricket team , played squash, did cross country for the school, went on outward bound courses , sat on school council, and was head boy of his house.
Of the three boys he was in year 6 with who had similar issues and went onto the high school, one is in prison, one is unemployed, I am not sure about the third. My ds has a good job with the local authority , has managed to buy his own car and volunteers with a national charity five hours a week . All it needed was a bit of individual attention, I volunteer to help boys like him in primary school but my heart breaks for them when they go to secondary because they support just isn’t there.