So it should be easy to find studies that prove that non-ADHD people that take it, have dramatically improved productivity.

It's very easy to find studies that prove that Adderall (etc.) improve non-ADHD people's cognition ability. And it's equally easy to find studies that prove otherwise. The parent comment is very spot on. You can find evidence supporting anything nowadays.

https://pmc.ncbi.nlm.nih.gov/articles/PMC3489818/table/tbl1/