Must be the forth theory then.
Also in the first thread you linked too they talked about how bullets are only effective for the sake of fair gameplay but its a general rule that if it happens in a cutscene then thats how the weapons function canonically. Near the end of the ending cinematic for the Evacuation Campaign we see the hunters mowing down several Monsters in a relatively short span of time. Those Monsters had much more firepower focused on them than usual and it was probably mostly headshots but it still proves that if anything bullets were made less effective for fair gameplay.
Just putting that up here because that thread is closed.