There is little doubt the Iranians have made some strides with their American acquired equipment. Though it's a hit of miss process of what comes up in availability. For instance their stock of 285 AIM-54 missiles was idled for many years. Until they clandestinely acquired new batteries. Some things they keep running out of sheer amounts of aircraft produced, like hueys and Seacobra gunships. Parts are easy to find. My understanding is that only about 33 of the Phantoms were airworthy. Folks incorrectly disparage the Iranians. They are quite capable and folks forget they have a complete USA built academy system. They are a credit to themselves really.
After the War with Iraq, and then years and years of not having the correct or enough parts, their old US aircraft are not very numerous and certainly, though they may fly and have some of those older systems still capable, are not nearly up to modern capabilities.
Do they need to be? Well, if they had to battle Iraq again, or say, Oman or something...no they do not.
But, if it were say Turkey or Saudi Arabia or Israel they went up against, they would fair badly. If were the US, there would be no contest.
So, yes, they are making do with what they can, and what they have...and they are being creative about it and do have quite a bit if industrial expertise, know-how, and capabilities. They should not be under-estimated,
Having said that, they are still significantly dependent on outside help for the more difficult and higher tech items, from their air defenses to numerous other programs.