Well, accordingly to Coram, Robert, in Boyd: The Fighter Pilot Who Changed the Art of War, a biography of John Boyd, it was pretty much a consensus in the USAF circles that all MiG aircraft were superior to their American equivalents. MiGs would outmaneuver, outgun, and be faster than any equivalent American aircraft, As an example you can compare MiG 21 operational records against F4 and F5 (smaller but still close to the same category as the MiG 21) during the Vietnam war Era. T

John Boyd and some other people would finally engage on the USAF/DoD projects that would end up creating the F15 and F16, the first US aircraft that were way superior to anything Soviet Union could fly at the time.

By the time F15s and F16s were entering service, the Soviets were decommissioning some of their older MiG 21s and bringing MiG 23s, which was a fiasco, into their service. Until the MiG 23 debacle, MiGs were known for being very fast, very maneuverable, and very powerful, while being straightforward aircraft as far as maintenance and mechanics went You could pretty much repair them with a screwdriver, a hammer and some steel wool. (Brings to mind the AK-47 assault rifle as another example of Soviet ingenuity)

Add on top of that the legendary fearlessness, bravery and ability of Soviet pilots since WWII and it makes the stuff of legend you see in flight simulator games.

That book (Boyd: The Fighter Pilot Who Changed the Art of War) is a good reading if you love military aircraft, especially fighters, to understand how US was finally able to overtake the Soviets on that field, and to learn about the life and ideas of the man that changed combat aviation and the whole way we wage wars today (OODA loop, Shock and Awe doctrine, so on, so forth).