There is a big difference in the ballistics between a 5.56 mm round and a .22 lr.
Yes, when we used to slaughter hogs at home we used a .22 LR round to shoot them in the head, which only knocked them out, then we cut their throats before they regained consciousness. Most slaughter houses do not use a .22 LR to kill animals. They either use a pneumatic bolt or a sledge hammer. It's cheaper and more affective.
IMO, A .22" hole is still a .22" hole no matter how fancy the gun it came out of. The ridiculous theory behind 5.56 / .223 is that "the bullets will tumble and do more damage". NOTE. RIDICULOUS. Yes this phenomena DOES happen, under very specific conditions (specific ammunition, specific barrel threading, specific barrel length, at a specific / narrow range, under specific environmental conditions, at specific depths of penetration, through specific material). Then you throw this wonderful round in a weapon that is a complete mechanical A hole... Boy, who wouldn't want to rely on
that to save their lives?!?
Benefits of a .22lr are commonality, price, recoil, compact weapons, low noise level, weapon and ammo variety, it goes on and on.
Benefits of a .223 / 5.56? .............. Shooting ground squirrels at long distances with cheap crap ammo, because 22-250 don't come in trendy black rifles?
To each their own though. I still say taking deer with head shots from .22's is
far more humane than any bow. But again, JMO.