The OP says it all. Cheap fares + expensive aircraft = doomed. In addition, unlike UA which operates onward to GUM and has the Island Hopper traffic, US had none of that.

Not sure there's many people who would fly WAS-CLT or NYC-CLT when they can fly xJFK or xIAD directly to HNL or, of they do need to connect, break the trip at LAX or SFO. That leaves CLT O&D as well as some Florida inbound traffic. But, have to ask why anybody would fly Florida-CLT-HI when they can either fly through ATL on DL or break the trip on the West Coast.