I have some sympathy for that argument, but I think we should still distinguish the cases and talk about them accurately. If the situation really is that 90% of people need some sort of intervention to reach the desired mental functioning, then we could just say that and argue for it openly; the pro-nootropics community makes those kinds of arguments, for example. I think when loaded terms like "abnormal" or "ill" or "treatment" are used, though, they're only really accurate if we're talking about pathological deviations from a species norm.

But actually my interest in what constitutes the "norm" is somewhat more basic; I think how human attention works is quite interesting as a subject of scientific study, and I wish there were more aggregate data on how it varies in different situations and across the population.