And what I'm saying is if they did, the gap would be even larger between them and people with ADHD.
It's not all linear like you suggest, though. There is a diminishing return in such cases where a person is naturally overachieving to begin with. And not simply because you can't do better than a perfect GPA, but because that person already possesses the necessary intellectual, social and organizational tools to achieve such things.
You are also sort of mischaracterizing the effects of the drugs, and their therapeutic benefits for those with ADHD, which is completely understandable considering they are sort of difficult to articulate to begin with. Yes, everyone gets some degree of enhanced focus, and focus euphoria. But that really only goes so far by itself, and can be acutely replicated with caffeine and other stimulants. For people with ADHD, the amphetamines specifically help fix a broken reward center in the brain which makes organization and initiating focus nearly impossible, and this effect is longer lived. It's difficult to explain, but for example, I literally cannot organize a space to the satisfaction of most people, even with the drugs. But with them, I can maintain a passable level of functional organization. And it's not because I am lazy or a slob or anything - clutter actually gives me anxiety, but I can't do anything about it. I can spend hours cleaning the house top to bottom, and be reasonably proud and satisfied with the results, but my wife will come home and spend another hour on it, and it will blow my mind at how much I missed. That's not a problem most people have, and even with the medication, I am considered somewhat deficient in that area.
Studying, test taking, etc - that's never been a problem for me. Like I said, I did pretty well in two years of undergrad without medicine. What became an issue was staying organized as the curriculum became less structured, and as I had to take on additional adult responsibilities. My hygiene suffered, and I developed anxiety problems - I wasn't quite to the level of keeping piss bottles and trash next to my bed, but I was on that path - 100% of my effort was put into school, because that was the priority. If I had to do anything besides study some day, then I would never start studying, and vice versa. The drugs, more than anything, allowed me to partition my time and focus on several things in the same day. Hell, even still - if I want a short boost of focus, I have some coffee. The drugs just keep me from turning into a cautionary tale on TLC.
Anyway, sorry for the wall of text. I hope I've managed to elucidate the issue a bit though. I really do understand where the resentment comes from, and I've had multiple discussions with therapists about the ethics of it all, as I've dealt with these same guilt trips many times before. I just hope you can try to see why there is a significant long term benefit in what the drugs do for people who really have the disorder, versus the short term performance boost "normal" people get from it.