"Now genuine question, does anyone local have an informed view on why Emirates have leapt ahead leaving EY and QR behind at MAN? Is it really the A388 effect?"
I don't think that's unique to EK at MAN, I can't think of any airport in the world served by all the MEB3 (excluding DOH and AUH !!) where EK is not out in front in terms of market share. There's many reasons for this - they fly to more places more frequently than the others, superior brand and market awareness wherever they are, the A380 factor, attractive and user friendly website, good loyalty programme, top notch lounges, in flight entertainment, and so it goes on. Plus of course they've been around the longest - to an extent the other two have always been playing catch up. Like them or not, EK is a marketing juggernaut and even though I often find them to be more expensive than the other two, they seem to have no problem filling their planes and staying ahead.
In MAN's case EK also garnered massive local brand awareness and goodwill by making MAN the first "regional" airport on the planet to get a regular A380. The publicity and public response to that day in 2010 was staggering, and massively lifted EK's profile in the region.