[justsomehnguy]

You have the advantage of seeing the successor tech. Nothing later of 117 uses the 'big poly' design, with B-2 as an immidiate successor and F-22/35 as a years later one.

There would be always a question why did they chose a flying iron design, but efficency clearly states it's not needed.

[nomel]

For all we know, there could be low poly panels under an RF transparent skin. The "efficiency" could be purely aerodynamic.