The recent MITRE US Air Force Aircraft Inventory Study says:
“An armed version of the T-X trainer could perform vital homeland defense missions that don’t require more advanced (and expensive) frontline fighters. The U.S. should therefore accelerate T-X purchases and produce the trainers along with an F/T-X configuration for homeland defense missions and likely export sales.”
F/T-X Light Jet Fighter for Homeland Defense and Export
Unlike overseas contingency operations, Homeland Defense aircraft operate in a permissive environment with a robust infrastructure. Using front-line 4th and 5th generation fighters for this mission is expensive and misallocates valuable service life that would be better used to train and conduct "away game" combat operations.
The Air Force will soon begin production of the T-X, a jet trainer designed specifically to prepare aircrew for 5th generation aircraft. This same aircraft can be adapted to economically accomplish the Homeland Defense mission by outfitting it with a radar, aerial refueling, a stronger wing for weapons carriage, and armament control. This can be done for lower acquisition, operating, and support costs than using advanced frontline combat aircraft for this mission.
Purchase approximately 400 F/T-X aircraft to outfit 15 squadrons to supplement the Homeland Defense mission. F/T-X modifications and U.S. acquisition will position this aircraft for foreign military sales to nations for which the F-15, F-16, or F-35 are either too expensive or too complex to operate, or nations desiring an economical complement to their existing fighters. The F/T-X light fighter will also provide further opportunities for shared training and operations with allied and partner nations.
A MITRE Corp senior principal systems engineer, David Gerber, subsequently said (on 5 September) that: “an armed F/T-X, if adapted to carry armament, onboard sensors, and air refuelling capabilities, could adequately defend the United States while being cheaper to operate than fourth- or fifth-generation fighters.”
Isn't a degree of performance important for the air defence role? Endurance to CAP, climb performance to get to height quickly, speed to intercept.....?