I believe the Saber-ll program was based on matching as closely to the capabilities of the F-16s, as possible with what technologies were available at the time. If I'm not mistaken, then Grumman's involvement was much appreciated for these reasons. Logically speaking, why would Pakistan Air Force try to co-develop a fighter based on a design which is inferior to the F-16s it was already operating? It wouldn't make sense at all to be doing something like that. Hence I disagree with the statement that JF-17s are based on the MiG-21s. If anything Pakistan Air Force would be using the F-16s as basis to design the Thunder. Also, is it no so, that Pakistan Air Force operated the F-16s long before it started operating the F-7s which are a derivative of MiG-21s?