The FAA should have pulled schematics directly from Boeing engineering during certification. And the FAA should have someone with enough technical expertise and experience look at them. And that person should have said "The submitted information by Boeing doesn't include full details on this subsystem."

Whether or not the Boeing test pilot highlighted the system for the FAA is a red herring. It's the FAA's job to find this, regardless of whether someone points them at it.

If the FAA doesn't have the technical staffing or expertise to do this, then that's the problem. Charging the test pilot is necessary, but not sufficient.

If the FAA infrequently performs this work (certification of a new aircraft), then flex in retired expertise! You can't tell me there aren't qualified, retired candidates (ex-industry or ex-FAA) who would have signed up for a year or two review. And all the better that they don't have career incentives!

Essentially, this is the FAA charging Boeing for not doing the FAA's job correctly.