Well reasoned response but I take exception to one assumption:
In some areas in aircraft airworthiness this is probably enough. The manufacturer builds an aircraft and produces a maintenance manual. Instructions are specific - "Install sump plug, part No x fitted with new O ring, part No y and tighten to z ft lbs". Under these circumstances, audit is easy.
No it isn’t. It’s just as challenging as flight operations and your comments are equally appropriate to engineering, and now software. My impression is that the then CAA lost the ability to audit/regulate airline engineering and maintenance around 1976 or earlier. A Qantas pilot acquaintance says much the same : “CASA turns up, we tell them bull****, they go away happy and none the wiser”.