That seems perfectly reasonable to me as a line of reasoning, and I'm not casting doubt on whether it could work.

With that said, I also wonder how many of those people had undiagnosed ADHD/if such studies involved screening for ADHD.

Unmanaged ADHD leading to consistent failures in life and other difficulties -> depression/depressive symptoms from the consequences, lack of achievement, etc over the long term, is a pretty common story.

And obviously, the responsiveness of those with ADHD to stimulants is pretty well-known.