I think a lot of this is the fact the armed forces have gotten away from teaching and stressing marksmanship over the years. Yes, they still teach it, but not with anywhere near the emphasis they used to. It's much the same with police officers today. A well placed .223 / 5.56 MM round will have devastating effects. But the shooter has to be able to place it.
I would fear a well seasoned marksman with a .223, far more than I would a boot camp graduate with a .308, who never held a weapon, let alone shot one until 3 months previous.