I would agree though that for US routes to work sustainably over the longer term, you would need to have at least some J/F traffic - but not to the extent that you need 100% load factors. There clearly exists at least some J/F traffic if anyone looks at the loads on EK flights to the USA. However, the Y prices I used above are for the cheap saver fares, which clearly not everyone on the plane will be buying - there will be at least some more expensive fare buckets purchased. For comparison, the flex Y tickets ex-USA price out at about 1900/2000 USD and flex J 9000/10000 USD. I believe there are some unfortunate forum members who have to pay those kind of prices
It may be that some people on ultra-cheap fares going from IAH-BOM are causing EK to take a small loss - but that cost would be more than made up for having just 1 J pax doing a rt. You can hardly sell J/F only on some routes and not Y - pax won't be having that...at the moment...
In fact 1 or 2 premium pax would more than make up for multiple super cheap Y pax on the same route. But here we are merging two models of airline operations - a per airframe revenue model and a per sector kind of thing. I think we should keep it simple and look at per airframe as that was your original point (A380s going to the USA).
And of course, no captain and flight or load dispatcher who wants to keep his or her job will allow a plane which is scheduled to leave with full loads take off with a full fuel tank - the art of dispatch is to put only the minimum amount of fuel into a plane (taking into account reserve and emergency of course!). So that saves on fuel costs as well. But for the sake of argument it's easier to illustrate with maximum fuel costs.