The P-47 wing, or What am I looking at?

[Kianoni]

Trapezoidal wings generate far less drag compared to straight wings and elliptic shape is basically the perfect trapezoidal design.
Why wasn't it used in much more broader scale for it's superiority?
Answer lies in production - elliptic shape was and is much more complicated and expensive to produce. I guess this could also be the reason for the airfoil to keep it's shape over the years - maybe they used the same production lines throughout the war?