Sorry, that's is all just nonsense. You can put improved components in any plane. The reason anyone uses MiG-21s for anything is they already have tons of them and are trying to salvage some value out of them.
You are not making sense. Pakistan isnt buying scrap Mig 21s to derive some salvage value out of it. Pakistan and China have been designing and building brand new modernized clones of Mig 21s such as the F-7 MG, F-7PG, FC-1 and JF-17s. These are not only cheaper alternative to western fighters like the F-16s but also comparable in performance.
“You can put improved components in any plane. “
Yes, and the difference is between putting it and not putting it on the plane. For the sake of our argument, my point was Indian Mig 21s have those systems and PAF older F-16s A/B dont. An old but uptodate modernized and well maintained fighter is any day better then a costly and poorly maintained fighter with no modern systems or MLUs.