My answer is more radical. I have seen a few A380 economic analyses which back me up. I think the A380 is more fuel efficient in most of its applications. How come? The A380 goes onto routes which are too big for one B777 and too thin for two B777. So if your required pax uplift is somewhere between 360 and 489, you are running one A380 against two B777. Ignoring cargo for simplicity, and doing the fuel use sums for 425 pax:
A380 178300 / 425 = 420 kg/pax, compared to:
2 x B777 = 2 * 112700 / 425 = 530 kg/pax
IMHO the A380 is a finely tuned machine which works economically in only a very limited spectrum of operations. Inside that spectrum, it works well. Outside that spectrum, it doesn’t. One doesn’t directly match the A380 head to head with a B777 – it is outside the spectrum of successful A380 ops.
The A380 aircraft is being taken up by airlines with the route planning sophistication to be able to match the A380 to a specific need and deploy their other aircraft (including B777) to complement it.