Unlike, say, the B-29, the B-17 FE position wasn't/isn't necessary to fly the aircraft around the patch in Hometown USA.
On the other hand, in wartime flying through fields or flak and attacking fighters determined to shoot you down, the FE was a critical part of the crew dealing with battle damage throughout the entire aircraft and it's systems, plus serving as a gunner, an extra set of eyes, and communicator.