I think you are a good example of a struggling, but clearly very engaged parent who is doing everything possible to ensure your child is supported well enough not to disrupt others. I am sympathetic and also believe that many on this thread are blind to the issues good parents of SEN children have. They are also generalising and dumping all ND children in together, when in fact there are multiple 'versions' of both ND experiences and ND parents, just as there are NT.
First, there's children who are clearly ND. But their parents, for whatever reason (lack of knowledge, lack of time, lack of resources, lack of interest, or simply that they're so worn down by the behaviour that they've given up,.or whatever) just don't seek support or employ the recommended management strategies. Their children may or may not have been able to thrive in ms but we'll never know, because they're the 'naughty' kids. And because the parents either can't or won't engage, this becomes a huge problem for the teachers and for other children.
Then there's the children whose parents know full well they're ND. They've done all the research, they might still be waiting for diagnoses (or even already have it) and they're fighting for every bit of support possible, both at home and at school. They're experts in ND, perhaps more so than many professionals. They will know whether their child could thrive in ms with the right support, or needs a specialist setting. The LA doesn't listen to parents, though. For these kids, successful inclusion in ms might be the right thing, or it might not. But while the LA is dragging its heels, delaying issuing EHCPs and generally not dealing with the situation, the situation gets worse and worse - for the child, their parents, the teachers, other children.
Then there's the different types of ND. My 8yo dd is on the autism diagnosis pathway and currently thriving in an extremely supportive (not private) mainstream school. We fought for her EHCP because her difficulties were very hidden at school and resulted in EBSA. She's well behaved at school, wants to do well. She's bright, socially motivated. And this week she's been home in tears twice because she's sitting next to a ND boy who sings and hums (noise triggers for her), and repeatedly knocks her glue stick down on purpose (a personal space and control trigger for her). She knows enough about herself now to use her personal resources put in place for her. So she used her movement break card so that she could retreat to the book corner for the remainder of the lesson.
My point being that some SEN children - who may fall into one of the above categories - become disruptive to all children, including other ND children. But I'm not going to sit here and blame his parents, because I have an understanding that it's not his fault, nor necessarily his parents' fault. They're likely victims of the convoluted and opaque 'system' that currently exists.
I'm very much in favour of inclusion in ms schools for well supported ND children who are, or are capable of, thriving - both the currently 'disruptive' and undisruptive ones. But 'inclusion' at the moment isn't working for anyone.