Mr Low,
I have 3 points:
1. During the "Cold War", BVR was seen as the way forward. Lots of weapons, on very fast a/c that were optimised for "Shoot 'n' Run" tactics....Oops, the wall fell over, and they were largely redundant. What came instead, were conficts, and policing actions that almost always required a VID of a Target. That is why, you could be forced into a turning fight: Because you have to get that close.
2. For every technology, there will quickly emerge a counter. "Over the shoulder" missiles with "smart" seekers will be no exception. As other posters have noted, if I am actually behind you, not even a Python 4 is a threat.....
3. No amount of technical kit, and helmet mounted thingy-m-jigs will deflect a well aimed bullet! A 9g-out-of plane break might. It's a "known" in the fighter communities all over the world that, it is rarely the chap you see (either visually, or on radar) that will get you, it's the other chap you didn't see.......hence stealth on F22.
Here endeth the lesson.....
(So WHY did we take the gun out of Typhoon?)