since there are no second-amendment implications whatever the outcome.
Except that it's the enforcement agency getting to write the rules it wishes to enforce.
This is not simple bureaucratic wrangling, it is agencies inventing policy by fiat. Which must needs be opposed at all turns.
This is not about whether you feel infringed upon, that's arguing from the specific to the general, this is about how all of us are to be governed. And, frankly, that matters.
So, yes, in that specific sense, I agree with you that this is not a Second Amendment issue. Because I find it a violation of all the amendments (well, except the 18th). If bureaucrats can create rules by fiat, especially in the face of specific laws, rules, and ordinances to the contrary, then the rule of law has no meaning. Baronies can be created, troops quartered in houses, property or liberty taken without warrant, worship of the Aldenata can be compelled.
From the general to the specific. If ATFE can make this rule, they can make one that bars non-FFL sales in AZ, too. And, once in the CFR, it is the law until forced out by legal contention--presuming that the contention against is upheld by a sufficient enough court. Examine Lautenberg, which clearly had "ex post facto" problems before enactment, and has run into further problems of late. It is still the law of the land unless and until it can be overturned.