What benefits of Adderall are you referring to?
Drugs like Adderall can have distinct adverse effects, like cardiac arrythmias, increased blood pressure, jitteriness, insomnia, anxiety. And drug misuse/dependence is a major problem with stimulant-class agents.
So for sure it's not true that everyone benefits from Adderall. Widely abused on college campuses, among non-ADHD students it has a small positive effect on academic performance and at higher doses is a distinct negative. OTOH for people with ADHD the right treatment (Adderall or alternative) can be greatly beneficial. (That is, ADHD treatment allows recipients to perform closer to their non-ADHD peers.)
Finding out if a person has ADHD requires evaluation by a qualified behavioral health clinician. Often it's not an easy diagnosis to make for even the best clinicians. Anyway I'd concur that diagnosis and treatment should not be attempted as a DIY project. Collaborating with a trustworthy practitioner is by far the best option.