The 787 is not an efficient domestic airplane. IIRC anything under six hours on it and the 767-300 beats it for costs.

That is the reason the '797' is being developed. It's essentially a 787 in size but doesn't have the structure to carry all that fuel so is quite a bit lighter.

Honestly I think they are using it domestically right now because they don't have other routes for it. This China stuff will make it worse if we pull it off those.