If I'm reading the parent comment correctly, I think they're saying that that the high rates currently being diagnosed require one of their three conditions to be true.
That is, if ADHD is accurately diagnosed, and never had an evolutionary advantage, and isn't caused by some modern factor, then why would ADHD be so highly diagnosed today? Which is an interesting thought in my view
It could share a root cause with something that was evolutionarily adaptive or simply not have been sufficiently maladaptive to be strongly selected against.
There are other conditions. There's at least a cultural component in that we haven't always embraced mental health care in the US as much as we do today. Many other parts of the world still don't.
Whether over or underdiagnosed now, it was underdiagnosed in the past.
That is, if ADHD is accurately diagnosed, and never had an evolutionary advantage, and isn't caused by some modern factor, then why would ADHD be so highly diagnosed today? Which is an interesting thought in my view