First of all, there's no guarantee that you will be able to use BVR. A stealth fighter using its radar is the same as a man in a camouflage at night turning on his search light. Everybody will know where you are. There might also be rule of engagement restriction, as has been many times that forced within-visual-range.
For WVR, the ability to supermaneuver is useful. It can give you that extra edge to get the angle on a target. You have to give up a lot of energy, sure. But you do have >1 TWR, and your buddies to cover you. It's not a magical tool but another one in a toolbox.
Also, in WVR, the advantage goes to the side with fewer planes. There was a study from the korean war to show this. The reason is because if you and your buddy is fighting 20 bandits, you can shoot at anybody that flies in front of you, while the enemies have to visually identify. And the speed of jet combat makes it impossible to verify before you lose your opportunity.
>So it might, might be useful if: both sides empty their long/medium-range radar-guided missiles at one-another, only two combatants remain, neither decides to bug out, the aggressor empties their IR missiles unsuccessfully, and the defensive craft is imminently going to be within the weapon employment zone for the bandit’s cannon
Yup. Just like in vietnam. We are gonna fly up there with our f4s afterburning to mach 2, then we will launch all our sparrows at the bandits, who would fly straight into our missiles because they are dumb, and then we will land just in time for lunch.