ohh one other thing. mig 21 was placed IN SERVICE in 1959. all those aircraft are much younger. F-15 might have been introduced in 1972 but it was put in service 17 years later in 1989! are you trying to compare 1959 technology to 1989?
i can look up other aircraft if you want me too, but im more then sure they were created to fight other planes then mig21's, as i already said thats what f-4 were all about.
iwas bored...
this are the countries that use mig21s currently. How many of them do you consider threats (besides almighty n. korea)? hell so you even know where they're located?

Algeria, Angola, Azerbaijan, Bangladesh, Bulgaria, Cambodia (grounded),Croatia, Cuba (most grounded), Egypt, Ethiopia, India, Iran, Laos (grounded), Libya (most grounded), Madagascar (grounded), Mongolia (grounded), Mozambique, Myanmar, Nigeria, North Korea, Pakistan, Romania, Serbia, Sri Lanka, Sudan, Syria, Tanzania, Turkmenistan, Vietnam, Yemen, Zimbabwe