The way that it is handled today, "ADHD" seems to represent a spectrum of symptoms rather than a well-understood root cause.

I've seen people go through school and adulthood, with different doctors vacillating between "you definitely have ADHD" and, "there is no chance that you have ADHD". Clearly something is up, and their symptoms broadly fit the guidelines, but the typical medication (amphetamines) sometimes seems to do more harm than good. "It helps me focus, but gives me no control over what I focus on" is a common refrain, even in this thread.

I am sure that accurate diagnoses have helped a lot of people, and I don't want to belittle that. Based on my personal experience, though, I'm not sure that "prevalence of ADHD" is a particularly useful label for large-scale analyses.