> and ADHD is kind of a weakly differentiated diagnosis that could apply to most people.

It's not, the problem is that it sounds like it because ~everyone faces some (way) lesser version of the struggles ADHD people face literally every day, many of whom probably do have some subclinical degree of executive dysfunction.

My personal thumb rule is that somebody is capable of finishing school, autonomously managing their living conditions, finding and keeping a job, and having at least a modicum of social life at the same time, they're high-functioning enough that they almost definitely don't have ADHD, or only some ultra-light version of it.