But for ADHD it doesn't just give concentration. It makes everything work properly. Emotions, Impulse control, Organization and so on. Everything that is controlled by neurotransmitters.
It improves those things for everyone else, too. While those symptoms are real, and have plenty of biological underpinnings, they are not distributed bimodally in some way that distinguishes ADHD from “just” having terrible executive function, time awareness, and so on. Same neurotransmitter deal for everyone else.
My point is that the pills cause a ton of extra neurotransmitters - that's the same for everyone. In the adhd brain it has an extra effect of giving the natural neurotransmitters a chance to be absorbed and fullfil their duty. That means that during the effect of the meds the person with adhd also gets to have a functional brain for things unrelated to what the pill affects directly.