[seba_dos1]

> We've given both groups of people the same label, "autism", despite the fact they have very little in common and clearly "don't have the same thing".

I'm not sure it's so clear. I've been lucky to be surrounded by people similar to me for a big chunk of my life which significantly reduced the feeling of "not being understood" or "from a different planet" and I don't have much trouble passing as a regular person, but in a severe meltdown I can still shut down and downgrade into something akin of that non-verbal kind of autism for some time. As far as I know, that's not how neurotypical people react to intense stress at all.

[skissane]

> but in a severe meltdown I can still shut down and downgrade into something akin of that non-verbal kind of autism for some time. As far as I know, that's not how neurotypical people react to intense stress at all.

I'm very sceptical of the existence of "neurotypical" people, but I think speechlessness, difficulties in processing verbal information, etc, are actually quite common experiences when under extreme stress, and many people who would never be diagnosed with ASD respond similarly to how you say you sometimes do. I don't think similarities between how some people act on those occasions when they are overwhelmed - whether they are overwhelmed rarely or frequently – and how other people act 100% of the time, really have much significance.

[seba_dos1]

> speechlessness, difficulties in processing verbal information

I don't think these words even begin to scratch the surface of the experience I'm talking about.

> I don't think similarities between how some people act on those occasions when they are overwhelmed - whether they are overwhelmed rarely or frequently – and how other people act 100% of the time, really have much significance.

It's very significant. Among other things, autism is a lot about what, why and how fast makes you feel overwhelmed (and sensory issues are just tiny little part of it). Learning how to identify when you're starting to get overwhelmed and how to cope with resulting meltdown is important part of therapy. As you noted, the word "autism" describes a pretty broad phenotype, but there are common patterns that simply don't apply to non-autistic majority, and which vary in their intensity across individuals. When everyday interaction makes you overwhelmed already, the difference between "those occasions" and "100% of the time" is not very sharp.

[skissane]

What you say is not true of everyone who meets the DSM-5 diagnostic criteria for ASD–"meltdowns", or "what, why and how fast makes you feel overwhelmed" are not part of those criteria–so it is possible to have ASD (per DSM-5) yet not have those symptoms, and indeed there are people out there just like that.

Conversely, there are people for whom what you say is very true, but who don't meet the diagnostic criteria for DSM-5 ASD, and hence officially don't "have autism". People with anxiety disorders, panic disorder, OCD, etc, can have very similar (if not identical) experiences, yet they don't have the right set of other symptoms to meet the DSM-5 criteria for ASD.

I get the impression you are defining "autism" anecdotally, based on your own personal experiences and those of others you know, or based on popular information sources (as opposed to the research literature). When you define it that way, you may actually be talking about a rather different construct from what the DSM-5 is talking about.