Some EK planes are configured for high-density Y (for example an extra seat per row compared to QF). Don't know what Y is like for the SYD-DXB-LHR sectors (have only flown F), but presumably it is the best that EK offers. Most likely it will be less comfortable than QF which has a stunning A380 Y config on SYD-LHR (maybe the most comfortable Y in the world right now), so the only reason to choose EK over QF is a substantial price saving, imho.