Flying pay for FCs is a bit of a contentious issue, which I imagine will be looked at pretty closely in the next FP review. It's constantly explained that flying pay is, in equal chunks, a recruitment and retention allowance. Recruitment in that it offers a little extra for doing a dangerous, difficult job with a long training pipeline, but I dispute this as I think most people who sign up as wannabe aircrew don't give a stuff what the salary is. I joined without actually knowing what it was, I seem to remember. Airman aircrew might make it more pertinent, being that it reflects a noticeable increase over another Sgt-level job.
Retention is more important, though. My flying pay goes up every so often to reflect the fact that as I get to the 2000hrs mark I could, with relative ease, transfer to a private sector job for 50% more pay, many more benefits, and none of the detractions of a service career, leading to a much higher quality of life. It's there to narrow the gap between my colleague who PVR'd and now flies for BA, and me, sitting there as a valuable 3rd/4th tourist, and make me less likely to leave.
However, I fail to see why fighter controllers need "retained" when the E3 jobs are terribly, terribly popular. Nor does it offer them the chance to jump ship to a more highly-paid civilian job like pilots can, requiring an increase in pay to keep them.
I'm very much in favour of the concept that flying pay should be paid to everyone who flies to reflect the strenuous, dangerous, complex nature of the task, and that the various bands should reflect some of the retention issues unique to each aircrew job (such as the availability of very highly paid civilian flying jobs for pilots), but the MoD will never admit that it's "danger money" nor will they say it's anything other than for "recruitment and retention." To that end, it wouldn't surprise me if it doesn't exist for jobs like ABM in the future. I suspect the disparities around the SO2 officer aircrew levels will need some money throwing at them, so perhaps it'll go to pay for that.