Function in what context? I have been diagnosed with ADHD at age seven. I have had many checkups and am currently medicated. I can tell you that I wouldn't need to if I didn't have to work a menial wageslave job. Interestingly I can focus perfectly fine when doing interesting stuff without medication and it has always been this way. What you are saying is that there is some proper definition of disorder, which would sensibly be defined relative to some "normal" human baseline. Tell me you know one "normal" human, why you see this person as "normal" and how it would be useful to use this as a reference for the big spectrum of human personality and mental fitness. I can tell you from experience that I didn't need medication when I wasn't forced to attend 12 useless meetings a week, use inefficient and stupid software and one would just let me get my shit done. I have quite a few friends who have had very similar experiences, and the idea of ADHD is just used to pathologize and medicate someone so he can work and be a "positive contributor" to whoever above them. Add here the necessary disclaimer that my experience is not universal and there may be people gravely suffering from it, etc. I do too, even with medication, but at least I can generate some bucks for management.

And what I know with ADHD is that the incapacity to handle dumb meetings is just one definition of functioning. Maybe you don't need medication to clean yourself enough to prevent skin issues, prevent addiction to substances, compulsive criminal behavior, avoid hoarding behaviors, have a safe living space, have the capacity to maintain friendships/avoid loneliness, engage with social interactions in a mutually respectful manner etc. But most people I know with ADHD severely struggle with at least one of the above and I consider that functioning, not just holding down a job. My understanding is not on the level of "can you do bullshit work" but it is "can you clean your dishes before they stink" and "can you respond to being turned down by a girl without blowing up your life".

I'd be willing to bet that there's some percentage of people who don't have ADHD, but they're also not capable of adapting to and meeting the unnatural demands school and work place on everyone and so they struggle in those environments where most people don't. ADHD medication still helps them overcome that difficultly and those medications can make a huge positive impact on their lives as a result. I'm okay with that.

Maybe we should have a different diagnosis for those kinds of people entirely and leave ADHD to the folks who couldn't accomplish what they wanted to do even if they never had to work, go to school, or follow a schedule set by another person. In the end though, what you call it doesn't matter. Both situations are thankfully improved through the use of the same types of medications. Medications which are pretty safe and can mean the difference between being able to support yourself or failing to.

I'm okay with a wider spectrum of people falling under the ADHD umbrella even if some of them don't like being lumped in with people who really do have an executive function disorder. Odds are good those people wouldn't like whatever new label doctors came up with to describe them either. It'll pretty much always carry negative connotations because ultimately, it means that you don't have it in you to do what most people are able to do just fine.