From what I had read, it wasn't that Iran decided to neglect their air force, but that sanctions and the reluctance of countries like China and Russia to actually deliver anything resulted in the focus on missiles and drones, which could be made and improved domestically.
The Iranian air force pulled off many daring and difficult missions in the Iran Iraq war when it still possessed good equipment.
Looking back at past few decades, the economic sanctions and the prohibition on providing aircraft and air defense to Iran were two things which undoubtedly hurt the country a lot.