I Think @
Oscar will expound on the kind of Air Force and especially doctrine, that PAF is with single engine aircraft and the kind of Doctrinal change twin engine, higher performance, range and genuine multi-role capablity suggest.
You have to look at the threat we face.. first. Then the requirements of facing that threat.. second.. and third.. the budget we have to meet those requirements.
The threat is not paper equipment but rather their employment. Like all Air forces the PAF keeps tabs on the IAF plans(and vice versa)..and based on these plans prepares its own to defend against. These plans are prepared knowing what budget the PAF has, and take into account mission effectiveness, survival of the force.. etc and then various levels of targets it has to accomplish in different hostile scenarios.
These plans are phased into the sort of posture the over-all airforce, the sector, the wing and the unit.
Will the unit be dedicated to defensive operations, offensive operations ..a mix.. etc
Once all these ideas are settled, then resources are allocated.. from what is(will be) available.
Hence, your doctrine comes into effect..
So if there are particular objectives such as disrupting a strike mission through interception or otherwise.. then this objective is carried out as effectively by a single seat light weight fighter as it would be a heavy one. If it entails providing close air support to troops from a base that is ten minutes of flight time from the border.. then a single engined jet will suffice.
Sure, having a big twin engined jet with lots of power is always welcome.. but not always needed. The UAE is still sticking to its F-16s.. so is the US with the F-35. Just depends on their operational requirements and doctrine. Had Pakistan the need to go and strike an enemy beyond 1000km and massive land to conquer or had it not developed ballistic missles.. perhaps that would make sense. But within its requirements to defend its airspace and provide support to the troops and stall the enemy's warmachine at the border.. its adequate.
I cant recall who, but I read of an USAAF officer who was asked by Gen Doolittle about the best bomber they had.. The officer replied "
The P-38".. to which the general was irked and annoyed.. and asked why? The officer replied..
"
because , it can carry two thousand pound bombs which are usually all that is needed for most targets, deliver them with better accuracy than most aircraft.. and carry this payload to Berlin and back.. And.. it can defend itself from fighters while cost much less than a B-17".