I believe they were purely symbolic. In some cases, epaulets were an exclusive feature of officer's uniforms although this is by no means an absolute. For instance, in WW2 EM service coats as well as Ike jackets had them as did the officer versions. The original M41 jacket had no epaulets, but they were included in the second pattern. The M43 jacket had them all along, as did its successors the M50 and M51. Interestingly, the original M65 did not have epaulets but this was very short-lived. The notion that A-2 epaulets were intended to keep anything but rank insignia in place is cut against by the fact that the epaulets are sewn down on both sides, which would require one to thread straps through the narrow openings. I'm not sure this is even possible with some types of equipment, and being strapped into a seat in this fashion would mean certain death in an emergency.