All:
Before I would go off half cocked about who will beat who......you must look at the "segments" of the airline business.
U certainly has a lot of business flyers who demand first class, upgrades, lounges, and worldwide service, and they make their bread and butter on those folks and at the same time carry lots of families on vacations. Legacy carriers concentrate on people who HAVE to fly for their job/work.
JB caters to more of the discretionary traveler, like the families who are on vacation and the occasional traveller. Of course, they carry their share of business people who have to fly to work and that is where the battleground, but their bread and butter is people who fly because they WANT to. In other words, they will fly if they can afford it.
I think they cater to different segments of the business. Some customers will choose one over the other. Some choose price, some choose schedule, some choose service. There is enough to go around.
This is all a mute point if jetA stays at $2.50-3.00 per gallon. There isn't a profitable route with that kind of fuel bill in the US.
A350