Well clearly a lot of prople disagree with me and that’s fine. I don’t think I have been ignorant or judgemental at all, although you were rather judgemental of me @Pinkyavocado 
What is it exactly that makes “mainstream schools” universally so very unsuitable for children with SEND?
We all have an idea of what a “mainstream school” is, most of our children attend one, and yet I guarantee each and every one of them is totally different.
I believe there is nothing fundamental about a mainstream school that means that children with SEND can’t attend, it’s just the way resources are allocated.
We no longer segregate people with learning disabilities (or mental health conditions) in secure homes and hospitals like we used to in the early and mid 20th Century. It is their human right to be included in society, we have a hell of a long way to go, but we are (slowly) becoming more inclusive and accepting of neurodiversity in this country.
“Mainstream” is just placeholder for “normal”. I know it’s controversial but this is AIBU so I’m airing my view that special schools are segregatory. Children are sent there with the very best of intentions and in many cases the children ARE happier and better educated there, but this is only because “mainstream schools” are often exclusionary (I say often because I have seen some fabulously inclusive ones, which is how I know it’s possible) and the practice of funneling resources to specialist provision is only making them more so.
The situation is highly unsatisfactory and I agree the system is broken. Parents are having to fight to get their children’s needs met. But whatever your child needs, be it specialist equipment, a smaller class, a quiet space, why not campaign for that to be made available in their “mainstream” school, as it should be?
Funding schmunding. If this pandemic has tought us anything it’s that there IS a f*cking magic money tree. It’s a question of whose needs and voices and interests get listened to and prioritised.
Children with SEND do not have strong voices, we have to advocate for them, and I will not accept the narrative that “everybody is disrupted” when children with SEND are educated alongside their peers.
They can be, and they should be, all that’s needed is proper resourcing.
The LA seem like the enemy, but as I said to the OP, my energy would be spent lobbying the local MP and launching a MASSIVE fundraising / publicity campaign to support my under-resourced local mainstream school.