Not much difference between 3rd gen and 4th gen fighters when it comes to BVR combat. Its all about the radar when it comes to BVR. 3rd Gen fighters had superior kinetic performance which is actually better for BVR.
So, if a J-8 is fitted with a modern AESA radar and associated PL-15, it will easily beat 4th gen fighters like J-10c just cause J-8 is much bigger and can carry a bigger and more powerful radar. It also outrun BVR missile much easier with its superior kinematic performance,
So, a J-8 with AESA can beat F-22 just like how J-10c group recently beat a J-20 with networking.