Are you sure it was a loop? The B-47 originally used a toss mode for nuclear weapons delivery. In the usual toss mode the B-47 would fly directly towards the target, at a specified point it would pull up and release the bomb at roughly 40º - 50º then continue pulling up until inverted then roll upright and depart the area.
As for flex the KC-135 has about 14 feet of flex measured at the wing tip if memory serves. I once saw a show where they tested a wing (777?) to destruction. If memory serves the wingtip flexed 24 feet before breaking. Next time you fly commercial get a window seat where you can watch the wing. You'll see flex in "smooth" air. If they buit a rigid wing you'd have a bumpier ride and a heavier aircraft.
Dan, U.S. Air Force, retired