I think you are conflating utility for humans and cost efficiency with energy efficiency. There is no question that birds are more energy efficient than planes

I think you are conflating utility for humans and cost efficiency with energy efficiency. There is no question that birds are more energy efficient than planes in terms of energy expended to move the same mass the same distance. However, humans would prefer to spend large amounts of energy by burning fuel to cross the Atlantic in 6 hours. It is much more COST efficient, but that is because energy is cheap.