I largely agree with you but it's not quite as generic as horoscopes and similar can be. Let's look at the DSM-V's diagnostic criteria for ADHD:
A. A persistent pattern of inattention and/or hyperactivity-impulsivity that interferes with functioning or development, as characterized by (1) and/or (2). B. Several inattentive or hyperactive-impulsive symptoms were present prior to age 12 years. C. Several inattentive or hyperactive-impulsive symptoms are present in two or more settings (e.g. at home, school, or work; with friends or relatives; in other activities). D. There is clear evidence that the symptoms interfere with, or reduce the quality of, social, academic, or occupational functioning. E. The symptoms do not occur exclusively during the course of schizophrenia or another psychotic disorder and are not better explained by another mental disorder (e.g. mood disorder, anxiety disorder, dissociative disorder, personality disorder, substance intoxication or withdrawal).
I think E is probably a common miss, and fits with ADHD being over-diagnosed vs. other disorders that can have overlapping symptoms. The differential diagnosis section could perhaps be more detailed. But now briefly looking at A's (1) and (2). (1) Inattention: Six (or more) of the following symptoms have persisted for at least 6 months ... (lists 9 symptoms related to forms of inattention, the most generic of which I think is just f: "Often avoids, dislikes, or is reluctant to engage in tasks that require sustained mental effort (e.g. schoolwork or homework; for older adolescents and adults, preparing reports, completing forms, reviewing lengthy papers)") (2) Hyperactivity and impulsivity: Six (or more) of the following symptoms .. (lists another 9 symptoms -- I count 3 pretty generic ones in a. (often fidgeting), f. (often talking excessively), and g. (often not waiting for a turn in conversation or completing people's sentences -- common in online meetings)).
While flawed I think this is enough detail to diagnose someone and clearly say "you're different", it's not nearly as broad as a horoscope "this sign is strong" or "that sign is deep" language and similar. The "Often" qualifier does a lot of work. Nevertheless, two people can both be diagnosed with "ADHD" and yet have few to no overlapping diagnostic symptoms.