I guess the fact that UAL has twice as many 777's as 744's has nothing to do with efficiency. If it is so efficient, why not buy more?
Both airlines utilize twice as many Narrowbody/RJs, not sure about the point you made...it is not just about your definition of efficiency...on 14+hr flights in which foreign ports are limited in slots...DOT wanted max pax and cargo capacity and the 744 wins. You don't buy more because you don't need more to do the few trips fitting this need.
Oh by the way, I witnessed a UAL 744 coming out of the Desert last month in Victorville CA; heading back to service w UAL when I asked the Airport Manager. There are a lot of premium seats on a 744 and when times are okay they make a lot of money.