The problem is real though. It stands to reason that the people that know how planes can be built safely are the one building planes; otherwise you could get in a situation where "those who know, build planes; those who don't, tell them how to do it".
There is a similar problem with financial regulation; my understanding is that the knowledge transfer between industry and regulation there is solved by the equally problematic "revolving doors", where people alternate between regulating and advising companies (and thus as regulators they don't want to make too many enemies).
Boeing merged with one of their competitors, and now outsource to subcontractors; both of these suggest the barriers, high though they are, are not insurmountable.
Also, the FAA could ask people from Lockheed to mark Boeing's homework.
The revolving door problem is mostly people coming back from a stint at a regulator to private employment at an salary that sometimes affect how beneficial their stint as a regulator was to the company hiring them post public service.
If that system was made one way so that people retiring from industry to government were forced to burn all "financial" bridges to the industry they were regulating by forcing them to accept a clause that they can newer go back especially not as a consultant a lot of those issues goes away.
There is a similar problem with financial regulation; my understanding is that the knowledge transfer between industry and regulation there is solved by the equally problematic "revolving doors", where people alternate between regulating and advising companies (and thus as regulators they don't want to make too many enemies).