To compare across the same airline, SIA long-haul configuration for the A350-900 is 253 pax in 3-class vs 443 in 4-class for the A380, so the A350-900 is carrying 40% fewer people and 1 less class.
Even against the most modern aircraft the A380's fuel consumption per pax per unit distance is likely to be competitive, the problem is filling the thing with people.
You know the seats are at the discretion of the airline, right? There’s no built in A380 first class.
Comparing the number of seats on an Emirates A380 for example is a bit unfair, because the upper deck is just so luxurious. If you remove the cocktail bar, the showers, and just keep standard business cots on the upper deck, you could probably add a good 20-30 seats
That would still be wrong. Most decent First Class cabins these days are on 777s: https://onemileatatime.com/best-first-class/
It's becoming increasingly rare for airlines to configure their planes with first class. However most (possibly all?) A380s were or are configured with first class, making direct comparisons more difficult.
Whether first-class exists on the (10 years older) 777 is neither here nor there.
Just a few weeks ago here on hn there was a discussion about this. Someone claimed the reasons A380 has poorer fuel economy per pax than A350 or B787 are
- older design with less usage of lightweight composites.
- older engine design.
- wing design constrained by need to fit within 80m box (size of airport gate apparently).
- wing design optimized for a lengthened variant (that was never realised).