F3G - that is a gross misuse of numbers! I could get a cheaper fare for the London/ Edinburgh/London train than the one you quote by simply avoiding train line and booking ahead, as you would need to do to get your £339 fare to NYC and back.
I am sure the seat would be more comfortable and have a greater pitch than any airline plus I would be spared some numpty reclining on top of me during meal service.
Please compare like with like if you want people to take your arguments seriously.
Shorter journies will always show a price disadvantage over longer ones because of the standing infrastrucure costs at each end which have to be bourne, no matter what the length of the trip.
The seats in economy are sh1t, ask any pax.
They are only tolerated because people have no choice when it comes to long distance travel.