In the United States, that body is the National Rifle Association who sponsor the United States portion of the International High Power Rifle (also known as Across The Course, or XTC) competition(s). See:
https://en.wikipedia.org/wiki/High_power_rifle One of the classes within High Power Rifle competition is Service Rifle which includes the AR-15.
So, since the NRA recognizes the AR-15 as a High Power Rifle, it's safe to say it's a Powerful Rifle
I was around, on the firing line, when the AR15 took over. The AMU started winning the National Championships with their highly modified M16's. The last year the Marine Team used the M14 as an XTC rifle was 1996. In 1997, I asked some Marine Team members how the 223 was doing, they said
about the same standing, better in the rapids, a little worse at long range". Cleaning the rapids is something the best competitors have to do, points lost in the rapids are points given away. The recoil of the 223 is so slight that groups actually get tighter and the X count goes up. The ballistic advantage at 600 yards was to the 175 SMK, but it was not a huge advantage over the 80 gr SMK's in use for the 223. Now if the M1a was chambered in a 6.5 Creedmoor, and considered a service rifle, a 6.5 will use about half the windage of a 223. If you analyzed the top ten, every one cleaned the rapids with high X counts, long range, a point or two difference. The winners won due to their standing scores. Standing really sorted out the great from the good. It has been said and it is true, that you win at standing and lose at long range. I have had excellent standing, rapids, and tossed it all away with eights at long range. And I am not the only one!
I will say, not everyone was happy about the poodle gun replacing the 308 M1a, myself included. But it was the service rifle of the US Armed Forces and it had finally been developed to a high level of accuracy.
However, once the Armed Forces went to the 223, they were getting their tails whacked at 1000 yards by civilians with M1's and M1a's. A score in the 180's is a pretty good score with a 223 and a 20" barrel. Many 223 loads are sub sonic at 600 yards, but at 1000 yards, that little bullet floats in the wind. The miltary teams had experimented with 6.5 twist barrels, tungsten bullets, but pressure is not your friend, and as in Hot Rods:
there is no replacement for displacement . So, the Military Teams got their retired Military buds on the NRA rules committee to declare the AR-10 a "service rifle". They did not want to go back to the M14 because the AR10 and AR15 are so similar, service members don't have to be trained on the manual of arms, operation, etc.
So the 308 still lives within the service rifle category.