There is no such thing as a single engine doctrine. PAF operated twin engined F6s until about ten years ago and B57s before that. It is about the role, operating cost and effectiveness. Twin engine planes like the SU 30s are maintainence, fuel and manpower hogs. F16s and even JF17 can undertake 2 or even 3 sorties in the time and cost it will take an SU 30 to do one sortie. PAF has almost 2 to 1 ratio of pilots to planes where as IAF has a shortage of pilots so it can maintain almost the same level of sorties as IAF with less planes. In an any case in a nuclear and missile environment there is no need to match aircrafts one to one. If one goes by historical analogy, SU-30s are like the Prithivi Raj's elephants and F16s and JF17s like Afghan ponies and we all know how that ended. In order words big is not always better. And finally the proof is in the pudding, IAF was not able to do any thing after the Parliament or the Mumbai incidents despite "superior fighters and superior numbers" except produce a lot of hot air.