Okay, so maybe plumbing is a bad metaphor, but I'll stick with it.
In a parallel situation, you need a different kind of plumber to fix a blockage, to a systern plumber, and then there are overflows that can be fixed yourself.
Problem is that all of the plumbers cost £800 just to have a look, or you can get it for free, but you might have to wait a few years. The people saying, "get the blockage plumber," say it with such frequency and conviction, that people struggling to manage their leaky toilet might feel like an awful person for complaining about the toilet, and even more guilty if they can't afford to stump up the cash. They might have the money, but they might get a plumber who isn't really qualified (and how would you know; the forums and recommendations are only good for the plumbers who say all toilets are blocked toilets, that's good customer service) and in the end, you might have to tolerate the leak, because the people on the Internet, and the (potentially) cowboy plumber, said it was designed that way.
And for the comments about gatekeeping; maybe I'm not great at communicating, so I'll try and say it a third time. I have no problem with people who are autistic being assessed and diagnosed (or with appropriately qualified plumbers giving their expertise). My problem is the misogynistic way that neurodiversity is used to make women put up with bad behaviour from friends or partners (yes, addiction is more common in people with ASD... is that an excuse? No!) or is used to undermine good, boundaried parenting with difficult children, and its common synonym, labelling children as ASD so parents don't have to do the difficult parenting.
Of course there will be exceptions, especially for girls, but mental health/SEN advice should be raised by teachers and health visitors etc, not strangers on the Internet with no real context or understanding of the family dynamics, history or motivation.