Our company had several situations where it took additional squeezes on the trigger to eliminate threats. It has to do with putting the bad guys down. M-16 takes 2 three round burst to drop someone, with the tiny bullets.
The AK is a larger round, that causes more damage in shorter range engagements. The M-16 round works best at longer ranges when it starts to tumble. In most engagements we are well within 150 meters. The round basically zips through them.
That's the point. It was designed to wound and not kill. Wounded soldiers require other soldiers to get them off the battlefield and out of the fight. Plus 300 rounds of .223 weighs about the same as 100 rounds of .308 ammo so you can pack more.
Tumbling ?
Please don't tell my you've bought into this.
The 55gr M103 and 62gr M855 are ballistically stable out to 800+ meters. There never is, and never was, any "tumbling".
Within appropriate ranges (300m and less), the M16 rounds will fragment much better than the 7.62mm alternatives, causing significant damage.