The main benefit to the USAF is that they are getting the same capability at much lower cost - they don't have to front up the cost of buying the aircraft, holding the spares inventory, or employing the aircrew and maintenance troops.
Even on the smaller scale of Draken providing the initial trial capability at Nellis AFB in 2015 after the active duty F-15C aggressor squadron had to be disbanded due to the dwindling fleet, the cost per flying hour was assessed to be 1:4 for Draken vs F-16C - more for F-15C. Going that route rather than rotating F-15Cs around to eke out the remaining fatigue life across the fleet also extends the life of the remaining USAF assets.
All explained here for those who still don't get it !
Draken Growth Strategy - Defence & Aerospace Report:
USAF video - original trial after F-15C retirement:
Air Force Magazine video on Draken Mirage F1 fleet regeneration, maintenance & logistics:
Draken ad video:
Draken documentary: