In fairness to both the FAA and Boeing, airplanes are becoming increasingly complex, particularly with mechanical, electrical, electronic interfaces. The increase in the requirement for very specialized knowledge makes it harder and harder to keep track of the unintended consequences of the introduction of new technology or changes to that technology.
Unfortunately this fact now exists in a corporate culture that incentivized short term cost savings and a regulatory framework that was never intended to provide oversight for these kinds of systems.
25 years ago an outfit I worked for hired a retired mechanic to help them out. His claim to fame was he had authority to sign out any maintenance release for every repair on any part of the Boeing 737-200. Structural, hydraulic, electrical, avionics, engine, everything. It was basically the only airplane he had worked on in his entire career and he knew the airplane so well he would get calls from overall around the world to ask for advice.
That kind of an aviation polymath is impossible to envision for any of the modern airliners. While I realize I am talking about maintenance, not design, the fact is the Boeing 737-200 was a pretty simple airplane and that simplicity made it possible to keep the big picture in focus. That is a lot harder today, especially when the only expertise for new technologies exists at the manufacturer and is proprietary.