There has never been a peer-level BVR conflict, so we don't really know how BVR will perform, when not being used against hapless Iraqi forces with dumbed down yesterday's planes.
The JFT in a war setting will carry 2WVR and 2 BVR. A very limited loadout. In contrast, the MKI has 12 hardpoints, can can easily carry 8 BVR. This means a single MKI can fire 2 BVR each at a flight of 4 JFT.
Estimates I have seen from certain USAF / LM posters suggests at about 30 kms, the pk of a missile will be as little as 30% probability of hit. With a little maneuvering and position, this would be even less. Closer shots may have a pk of 50-60%.
In this scenario, MKI flying in high and fast, can shoot and scoot, come around and shoot again, multiple times, as it has the fuel to stay in the fight. The JFT will be lower and slower, and will very quickly bingo fuel and return to base, needing to be replaced by another batch.
This is why a better fighter is needed in the longer term, with not only FLANKERS but Mirage 2000s, Rafales and possibly F-16s / F-35s / PAKFAs...
Would be a very big disadvantage for Pak.
This is why J-31 is not a good solution for PAF, as it is not designed to fight the Hi-hi battle at 400 FL+ at high speeds. You need an aircraft optimized to fight at those altitudes, with corresponding wing loadings and EM performance.
The closest plane today for such a role (available to the PAF) is the J-10, aerodynamically. Unless PAF can go for the Eurofighter or the Su-35. But the J-10 is not stealth, so it would face difficulty against the next gen. Which is why project Azm is so important.