I think you're putting the cart before the horse. "Adhd" is a code we use, a communication tool.
There's no benefit to thinking super hard about what "adhd" means, the benefit is to just using the word to help people. Yes, researches should think super hard about how to help the people the study, but the four letters adhd are just four letters, not some kind of truth we must derive.
Personally, i think we could just stop using it. The way experts use it, they all agree adhd can have wildly different expressions and causes, so what's the point? If a person is having problem that psychology and/or psychiatry help, then great let's get that help.
But if you and me both have "adhd" and we both have very different behaviors/symptoms and causes, then what is the usefulness of that terminology??
Adhd can be neurological (e.g. genetic hormonal imbalance), psychological (childhood trauma leading to long term anxiety and focus issues), or even physiological (poor nutrition/sleep).
So adhd may just be a symptom even vaguer than a fever that has a myriad possible causes and expressions. Am i a fever person when i have a fever? How is that terminology helpful?