The F-5 was always a second tier fighter even when it was new. That is why the PAF rejected it completely and forced the USA to transfer the F-16. It was always inducted to maintain force levels rather than provide a qualitative edge. The MIG-21 was a leading fighter when it was new, but it remained in service long after its successor, the MIG-23, had been retired and has mainly performed as a second tier fighter.
The current versions of the JF-17, the Block 1 and Block 2, are interim types which the PAF did well to induct as replacements of the older jets. The JF-17 is still being developed, and as a package it offers much potential for growth.