ADD isn't necessarily about school; it's about having the ability to pay attention and structure thoughts into actions. I was diagnosed with ADD at a young age and thought it was bullshit until I got to college because I was smart enough that I didn't need to pay attention to get good grades. When the ideas I needed to pick up were complex enough that I couldn't infer them on my own (data structures, anyone?), I noticed that I would listen intently to my professor in a class I enjoyed and come out with no idea what we just talked about.
Now in the "adult" world (it disappoints me that many adult are overgrown children), I know ADD is real because I'm certainly smart enough to write code that implements business rules, but I often lose track of important conversations. I constantly end up asking not for clarification of a topic, but just to hear things restated verbatim because the words went in one ear and out the other.
Your psychiatrist may be an irresponsible dirtbag that just throws stimulants at everything that comes through his door; incompetence is rampant in every profession. This does not mean that the body of established evidence for the existence and treatment of ADD is wrong.