Allow me to step in, the reason for going for additional f-16s was solely because PAF has decades of experience and considers them as an ideal multirole fighter that suits PAF combat style. Remember, JFT is a MAINSTAY fighter and f-16 is designated as a FRONT LINE fighter in PAF till the FC-20 comes in. There is a reason we didn't go for a huge chunk of blk 52s as a superior capability will come in a few years time in shape of fc-20 but the importance of f-16 will not be negated even then. Old f016s are being updated as the blk 15 is near obsolete and needed a new lease of life in shape of MLU-3 upgrades and so it gets and remains a viable threat to the adversary even after 30 years of its induction.
Regarding rd-93, it has proved to be a capable and versatile engine for JFT and so far PAF is happy with its very quick response time and fuel efficiency as well as appropriate thrust. The notion of it being under power is curtailed after Zhuhai performance but there is always a second option in shape of ws-13 which is being tested in China as of now, has higher thrust, better FADEC control but slower response time than rd-93.