On a more basic level before even getting to treatment, imo it'd be useful to have more studies on what the distribution of some sort of trait called "attention" is in the population to begin with, perhaps in various common situations. That might provide some sort of baseline: if, for example, 90% of people have "abnormally low" attention by some measure in some situation, then the definition of "abnormal" is probabl…
If people want themselves/their children to think/act a certain way, and this opinion is widespread, then it's completely valid to treat that as the target, even if 90% of the people in society need to be chemically modified to make them act that way.
Evolution isn't perfect, and at no point has it tried to optimize for happiness, it only goes for reproductive success, which we as individuals don't care too much about, at least in the short term. If there are interventions that we can impose that better optimize for happiness than letting us exist naturally would, we have no reason to avoid these interventions.
That said, I have no idea what the optimal desired mental function would look like...