Yes.. While B17s COULD carry 17,600lbs, and that would cut into range, I don't think they wanted them to, due to the altitude they were flying at and the air density (less lift) at 25000 feet. Also I think the idea of saturating the air with bombers meant less bombs per plane, but more planes. This was also seen in Vietnam with F105 Thuds, most of which were only carrying a few bombs on missions, when they could carry 5 times more. It was a matter of "don't put all your eggs in one basket" (that type of thing)