BigG, you mentioned Ayoob (not by name) for making a variety of statements pertaining to getting arrested because of the ammo used (reloads for example), gun modifications, etc., in a defensive shooting. Folks often bow to the reasoning as being fully correct or real because Ayoob is an authority and authorities know what they are talking about. This is a type of reasoning fallacy called an appeal to authority where the authority is to be believed when there is no evidence presented to support the position other than attributing it to the authority.
Another classic appeal to authority, actually an appeal to a disembodied or deceased authority commonly done in some of the gun discussions is to attribute aspects of design, use, and intent of John Moses Browning's 1911 guns. People will claim that JMB intended for 1911s to be carried in Condition 1, but such information has never been substantiated as Browning apparently never recorded such a statement for us to verify. Another is that JMB designed the perfect combat handgun and that if he didn't put certain features on his 1911s, then those features are not needed now. JMB's 1911 prototypes, however, have many differences from what became the 1911. As I recall, the military specified somthing like 46 changes to the gun before it was adopted. In other words, the 1911 design is not solely JMB's at all, but an adaptation of his design to meet ever changing military specifications.
Ironically, while you noted the shortcoming of the appeal to authority, you did the same thing. There is little doubt that there are all sorts of myths or legends about firearms that are not true, but by simply stating an opinion that the myth is not true does not actually debunk the myth. To debunk, you would need to provide data to substantiate your hypothesis. This is definitely the case in your argument that civilian and military ammo are not different. With no actual evidence, you are committing a fallacy of faulty generalization. This may also be a fallacy of the appeal to authority where you are treating yourself as the authority on the matter and as that authority, you consider the statement to be correct.
Additionally, while reloading books may not say military brass is 10% thicker and that you should adjust your powder accordingly, this lack of information does debunk that the rounds are the same. An absence of data neither justifies or refutes such claims. In rhetoric/logic, this is a fallacy called "affirming from negative."