I agree. I've never had much faith in the 5.56, despite what the critics said. I don't think that the ammo weight is as big a factor as it was in previous conflicts because the soldiers did most of their travelling in vehicles and didn't have to worry about packing 10 lbs of ammo in a 40 mile a day hike.
The 5.56 may have adequate stopping power at ranges inside 100 meters, but beyond that it isn't nearly as capable as the 30-06 or 308. Many of the engagements in the desert were well beyond the effective range of the 5.56 and the bad guys with the AK-47's had a clear advantage.
The bad guys did not have a clear advantage. 7.62 Warsaw has poor ballistics and AKs are not particularly accurate at long range. If someone's ever seen one place at a highpower match, let me know. 7.62 Nato, on the other hand, has excellent ballistics. But you point out what should be a well known truism by now: you can't have one caliber or weapon do everything well. With the correct ammunition for the twist and the target type, the 5.56 has shown itself to be very effective in CQB and urban warfare distances (anyone who disbelieves the lethality of .223 on man-sized targets may wish to look at the fatalities rate of aimed 5.56 fire in the DC sniper shootings). On the flip side, the superiority of .308 is (one would hope) pretty universally acknowledged at longer "sniping" ranges.
The one-size-fits-all mentality may simplify logistics, but that's about it.
You are mad. The 7.62x39 is ballistically inferior to the 5.56x45 just about anyway you slice it, but particularly at longer ranges. The AK-47 has a shorter effective range than the M16. Bullet diameter doesn't tell you much about the ballistic performance. The 7.62mm bullet is actually an inferior selection for the .308 case; you'd be better off with 6.5mm +/- 0.5mm.