There are plenty of good arguments against enhancement-style use of stimulants, but to suggest they don't do anything more than decent rest is just silly.
I think the parent’s point about it being the biggest relative increase in cognitive function is correct.
I can't focus or perform adequately at all without my medicine. I didn't get diagnosed until 28, so I have a lifetime of evidence to back this claim up. And once I started taking meds, I went from a depressing career I hated to spending significant time and effort self-teaching programming and computer science in the evenings while working full time, and eventually changed careers. Something I absolutely never could have achieved without medically prescribed stimulants.
But it's really hard for me to take my experience as someone with a neurological disability/impairment, and try to apply it to other people without that impairment. For instance, even with my condition, there is a very delicate balance that has to be achieved with dosing. If I take even a little bit too high of a dose, I am hyperfocusing in a way I can't control, and on non-productive tasks. Spending three hours furiously rearranging books alphabetically is not productive. And since "normal" people don't have the same deficits that I do, I genuinely feel like have those people take any significant amount of stimulants would do something similar. I was around plenty of people who "used adderall to study" in college but clearly didn't actually have the condition. Let's just say "studying" tended to involve many things that weren't actually studying.