Executive function is historically entirely a psychological concept, although there is starting to be some biological understanding which came later (e.g. which brain regions are involved, etc.).

Erm.. welcome to psychiatry ?

There is nothing bizarre (or unique to ADHD) about picking from a list of precise, agreed-upon criteria to form a mental health diagnosis. It's how the entire field works, and it's actually a huge step forward from the times when each therapist made up their own definitions.

In the absence of definite imaging or genetic markers for most illnesses, building consensus on criteria and thresholds in a reference manual (the DSM) is the next best possible way to end up with objective, useful and standardized definitions.

Not having a blood test for an illness doesn't mean it isn't real.

> It's important to be aware that each percentage point is hundreds of millions of dollars.

You don't need to resort to conspiracy theories once you understand the above.