at least on certain routes for me the one way icelandair J fares are half of what any of the big 3 want. Like im flying DUB-ORD(-AVL on a separate ticket) next year and when I bought tickets AA wanted $4k($6k if i wanted to go DUB-CLT), UA wanted $3500, Delta was reasonable at like $2500(DUB-ATL) but FI was $1400.