You should never be too hard on yourself, but putting labels can also be dangerous, as people often use it as an excuse to not work towards improving themselves.
Why can't I do what they can? Without a diagnosis, the answer to that question can be "because I am a failure as a human being", leading to erosion of self-worth. But being able to answer "because I have a handicap" (due to the mental condition) helps think more constructively about how to work around the handicap, rather than just expect to be able to overcome it.
In this thread, there an insightful comment that reads: it's like realizing that you are short... after decades of being told that the only reason you can't reach as high as most people is because you are lazy.
When you said "people often use it as an excuse to not work towards improving themselves", that is exactly what the author of the comment meant by "being told [that they're] lazy". No matter how much a short person "work[s] towards improving themselves", they will not get taller. They instead find ways to work around the issue, like carrying stepladders with them.
Keep in mind, that if we had never invented glasses, a huge swath of the world's population would be considered to be handicapped. And the ones that weren't, who have only experienced poor eyesight due to dust or tears in their eyes (temporary conditions, just like feeling sad would be in comparison to depression), they could very well share your attitude, and insist that people just need to "look harder".
However, I was thinking more about people labelling themselves internally, which is what the linked article focuses on. In that case, thinking of one's self as handicapped can be beneficial, which is what the article presents example of.
Since there is a medical professional involved in the diagnosis, they should be able to steer the patient towards the mindset that would be most beneficial for them, given each individual's circumstances. Repeated sessions work towards helping psychiatrists figure out, as you say, "which exact behaviours can be attributed to autism and which to personal development", and they can advise accordingly.
Minor nitpick: you said "psychologists", when "psychiatrists" would be more accurate. The latter are medical professionals who have gone through at least 14 years of study and practice, including a residency at a hospital, and they are the ones who are able to diagnose and prescribe medications. They are doctors, in the full sense of that word. Psychologists are not medical professionals (but that doesn't mean they're not useful).
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> In this thread, there an insightful comment that reads: it's like realizing that you are short... after decades of being told that the only reason you can't reach as high as most people is because you are lazy.
> When you said "people often use it as an excuse to not work towards improving themselves", that is exactly what the author of the comment meant by "being told [that they're] lazy". No matter how much a short person "work[s] towards improving themselves", they will not get taller. They instead find ways to work around the issue, like carrying stepladders with them.
Or summarized more concisely: One needs a diagnosis because other people are simply a##holes.