It comes from the Chief of Staff of the Air Force, Gen. Mark Welsh:
As Chief of Staff Gen. Mark Welsh visited airmen in Hawaii and at Kadena AB, Japan, this week, he emphasized that the service is committed to seeing the F-35 program to fruition, as the fifth generation fighter's success has great implications for the Air Force's role in future conflicts. "The F-35 is flying, it is a real thing, and progress is real," he said. Several countries, including Russia and China, are working on fifth generation fighters, he said, and even if the United States does not go to war with these countries, it will inevitably have to confront the military technology they sell to others. Extending the service lives of fourth generation aircraft, and even supplanting the force structure with generation "4.5" fighters, does not solve the problem. "When a fifth generation fighter meets a fourth generation fighter—[the latter] dies," said Welsh. "We can't just dress up a fourth generation fighter as a fifth generation fighter; we need to get away from that conversation," he said.Emphasis mine. It simply stretches credulity to think that aircraft as capable as the 5th generation fighters will be significantly threatened by the old technology of the 4th gen (or even 4.5 gen) fighter. As we've mentioned here, air warfare is about to change in a revolutionary manner with the full fielding of the family of 5th generation fighters. Pretending the old standards of air warfare still rule won't change the new reality their fielding will bring, and Welsh understands that.