We're also not talking just FMJ fighting ammo here.
Having owned a couple of AR10 rifles in .308, I can tell you that I'd rather fight with a 5.56 with expanding ammo than a 7.62, unless you are maybe talking about some very long distances or armor. Self/home defense against criminals? An expanding 5.56 in a torso that's only 5-10 inches deep is going to be bad news, like shooting a broadside yearling deer. or an 80lb pig. Not sure a .30cal is making any difference there, except being harder to shoot and toting less ammo.
