The definition of 'supercruise' seems to vary a lot
Au contraire, I think it's universally understood to mean 'able to sustain supersonic level flight without reheat'.
Lt. Col. Hank "Hog" Griffiths is also quoted as saying the f-35a will do M1.25 in dry.
No he isn't. He is saying that it can get up to M1.25 in reheat. When you cancel reheat, you are (for a moment) doing M1.25 in dry power. By your rationale, a Tornado F3 can do M2.0 in dry power!
Arguments about how long it takes to slow to subsonic speed are irrelevant - if you cannot sustain >M1.0 without reheat, you are not supercruising, even if you cover 150 miles during the deceleration.