The 5.56 is a great round, as someone said, against coyotes. Ask someone who has BTDT, 9mm and 5.56 both suck at initial take down power. Sure, you can kill someone with a single shot, but they won't be immediately out of the fight.
Remember talked to an SAS guy back in the day who was responding to a situation where a guy, who was not on drugs, took over 30 rounds center mass with 9mm, and he was still running away. Sure, he was already dead, but his brain didn't yet know it. Took a sledge hammer to his face in order to take the guy down.
Heard similar stories about 5.56, taking 4+ shots to effectively eliminate a threat.
Never heard of the same problem using 6.8spc or 7.62(x39 or x51).
The M468 is basically a Barret made M4, which they themselves stopped attempting to promote for military use since it still used DI and was largely no better than a run of the mill M4. Their latest hedge for military adaptation is the REC7.