It's simple you're balancing the on the assumption that only bad players play it.
You have no consideration for players who will actually hit the perfect kill time for a weapon consistently.
That is why you (343) think the BR having a .4 second slower kill time compared to the DMR and carbine is balanced is still "balanced"
That is why the max kills per magazine is lowered because of this assumption no one will get perfect accuracy and the extra ammo is just there to spray and pray with.
With this mindset, sure 14 rounds is fine and balanced but again there is no consideration for players who don't or rarely miss.
You're wrong and you are bad at explaining things. And talking to people.