thanks a lot for your insightful comment. I agree with you to some extent. I must point out that still many Iranians are going abroad to get university degrees from 2nd and 3rd tier universities, even though there are ample capacity inside Iranian higher education system. Most people who go abroad, education is just one factor. there are many other reasons that are motivating them to go to countries you just mentioned, education being one of them.
My argument is that Iran's educational system should NOT invest in increasing the quantity of its domestic graduates (this has been the focus in the past decades). Instead they should increase the quality by hiring top professor (which means higher salaries), focus on R&D, and so forth.