I haven't seen anything credible in this thread that actually casts real doubt on the ability of the 5.56. If you look at just about every western military, elite police unit, etc, they are using this exact combo for CQB. The HK MP5 has largely been phased out. There also hasn't been wide-spread adoption of alternative calibers such as 6.8mm or .300 BLK among these units either. Obviously there is some serious inertia among something like an entire military branch, but if 5.56 and the AR-15 didn't work, it wouldn't be the most prevalent system of choice, even among those who DO have a choice.
A lot of the more elite units in the US military started using Mk262 ammo if I'm not mistaken which is a 77-gr open-tip-match projectile, extremely similar to the Hornady TAP 75 BTHP T2.
A lot of the more elite units in the US military started using Mk262 ammo if I'm not mistaken which is a 77-gr open-tip-match projectile, extremely similar to the Hornady TAP 75 BTHP T2.