As ever I suspect it depends how you define sortie rate. You could just define it as getting airborne and landing again (I suspect a USMC view) or you could look at actual time on task, possibly at range (theatre-wide), in which case range/endurance become more of a factor. Without knowing what definitions each are using it is an impossible debate to have.
I am still very dubious that F35 will be able to operate at any sort of decent tempo from an austere site. Of course the US definition of austere and UK definition are probably not the same...............