Right it has to be sustained supersonic flight, which means you have to have a supersonic cruise speed. Otherwise you might as well burn up half your fuel on afterburner going high Mach number, and fly at your normal cruise speed the rest of the way. And the JSFs cruise speed is set below the 1.0 mark. Which is understandable in the USAF high-low mix with the F-22 in service.
It's too bad the Growler probably can't keep up with either one. It will have run out of fuel on ingress.