Ken,
Really. I hope I've made it clear somewhere in the last 415 pages that, as we say, it depends. If you can indeed decide the fight BVR, or either avoid the merge or blow through it with HOBS weapons, you may not need platform agility.
See here for instance:
http://www.pprune.org/military-aviat...ml#post9031874
But the F-35 cannot be stealthy and carry a HOBS system and its speed is inadequate to provide a decisive advantage over likely adversaries.