@UKBengali
Why would you think a fighter needs maneuverability in 2020? BVR combat is simply flying at high altitudes at mach 1 or so and launching from 70+km away.
Two reasons:
1. Give as much energy to the missile so it can travel further - that is why you would want to be travelling at near enough Mach 2 before you launch BVR missile.
2. More chance of dodging missiles fired at you.