Yeah, but without any case law all we really have in this opinion is a vignette of what the FAA will likely attempt to argue in any case that comes before them.
That's very true. However, very seldom will the ALJ attempt to work contrary to a legal interpretation, particularly one that merely defines the regulation. The most an airman could hope to argue is that he "thought" he had complied with the regulation and that he had gotten enough proficiency from the approaches he did, but he would need a very compelling reason to have not complied with the regulation and the interpretation thereof.
The legal interpretation carries far more weight than an opinion, even though it may say "we believe." It is the Administrator that prescribes the regulation, and it is the administrator that both interprets and enforces the regulation. It is the airman that is guilty until proven innocent. The airman cannot argue that the regulation is not fair, but only that he or she is not guilty of inconsistency with the regulation. Further, case law, such as it is in administrative law, is far less "binding" and influential than in civil or criminal court.