I think you're in a difficult place emotionally, so I'm trying to cut you some slack on the borderline offenceive attitude towards a disability. I'm an autistic adult, but wasn't diagnosed until after my autistic children were, which make me very aware of their needs, how they are suported, and the impact of this in contrast to how been unsupported effected me.
This I'd just a few examples of what diagnosis has given us:
Understanding of ourselves, not just in terms of 'why I find things more difficult' but the next step or 'this is what I need to do to manage that'. Eg. We can pace our plans to avoid anyone being overwhelmed.
Helpful in working out where disregulation is coming from. Eg. There are some senses DC seeks to regulate and others they are overwhelmed by, by knowing this I worked out that when they start putting things in their mouth, it's not about the tast, it's about drowning out sound, so ear defenders or moving somewhere quieter are more effective then conversations about germs/choking hazards. I would never of made that leap if i was thinking about the chewing as a querk without the context of autism.
Community, we are able to access a sen or autistic groups, so DC grow up with friends who are like them, instead of feeling like an outsider
School suport, I was overwhelmed and learned very little in primary school, still couldn't read or write when I moved up to secondary school. I did eventually catch up, but could probably have gone much further if I hadn't missed out on half my schooling through sensory overload. In contrast, DC have EHCP's, they get to go on movement breaks or work in quieter areas and are thriving.
Better mental health, a child with SEN is going to be corrected 100's more times then their peers. They're going to notice, and if they don't have a reason or have been told 'their personality' is to alway get things wrong, that's going to destroy their self esteem.