I'd tend to agree with you in many cases, but not all, based on my experiences coaching my now-8 yr old son's baseball team.
We had a kid on his team last year who had ADHD (or at least some affliction) and it was severe, and it was not a discipline issue. He was not a bad kid and by the end of the season he had really grown on me.
But sheesh, was he tough to coach. On some days I had to literally stand next to him in the field to try to keep his focus on the game. Sometimes he couldn't even hold the bat up to swing. Other times he'd hit the ball and run to third base. If you bat 3 times in a game and you know to run to first base the first two times and you run to third the last time, something's wrong. Some games he would be quiet and lethargic and others he'd be hanging on the fence in the dugout.
I really felt for his parents and they were very appreciative of the extra effort the other coaches and I gave to him.
Do I think people jump to the ADHD conclusion too quickly? Yes. I think some doctors may be giving these drugs out "upon request" rather than diagnosing an actual problem (if it can really be measured). But I think there are kids who really have problems.
I assume while you were coaching, the kid was severely drugged up...Wonder what he was like without the drugs...