Bingo, bingo, we have the case made in totality now. I'm a bit old fashioned and ancient, look at things from the old way. The line infantry weren't marksman ready to accurately throw musket balls with 100% hit rates into the enemy, they were spearmen with smoothbore muskets who killed through sheer volume of accurate kinda accurate gunfire en masse. You weren't counting on 1:1 hit ratios for shots fired, you were relying on the shock effect of firepower and the casualties that would occur from somewhat accurate fire hitting the enemy. Things ended up being decided by bayonet anyway, but fire played a roll, and it was based on general effect that can be made better by improvements.
Nothing has changed in a certain way, I suppose. There is such a high rate of fire today that nobody can hardly get their heads up to fight back and shoot straight, most killing is artillery, mortar, heavy machine gun medium machine gun, ect, air support, big gun power. The rifleman now uses his general rifle fire to suppress, intimidate, force back, cause some casualties and in some cases actually fight the way an infantryman can with is rifle in rare circumstances, but again we're back to generally effective mass fire to attack the enemy through suppression, shock of firepower, and some direct killing of the rifle. We are back to square one.
The issues come down to problems of ineffective fire and its inability to suppress and shock, then finally its inability to hit enemies at all. Green peasants thrown into a war they don't like might run from the sound of gunfire being fired into the air by the enemy; however we can see that experienced and elite troopers eventually become hardened by battle and will become less easy to shock and sometimes to even suppress. Sometimes hardened soldiers can tell where the gunfire is coming from and how close it is, how effective it is, how potentially lethal. If the suppressive fire is too far away, if its too weak, if its took ineffective, the impacts are far enough away sometimes the effective solider can take advantage of this and actually try to fight back against poor grade volume of fire. Simply put, if the bullet impacts are too far away, some soldiers will know the enemy cannot see or more likely, cannot effectively hit them, making them bold enough to try to use effective fire to shoot back. That was seen in some of the hardened boys in Afganistan now wasn't it? Some of those guys knew they were being shot at and didn't panic. When the more competent ones knew the enemy was out of effective range they might hold themselves together to take pot shots at the soldiers instead of panic and throw shots. While 5.56 might rain randomly, lightly, inaccurately around them, they might realize how poor the fire is an actually hold and shoot accurately back.
This is the general argument of the battle rifle squad and the DMR at the least. The whole point is a squad of men with M-14's, not special ones just general off the rack rifles, FN FAL's, G3's, can lay far superior effective fire at 600 yards, 700, 800 yards/meters and the cartridge itself combined with the modern line infantry firing it half accurately enough means the general suppressive fire is more generally accurate and thus better suppressive fire to pin the enemy down. The battle rifle squad is going to be better at letting the enemy know you're rounds are in the vicinity and the fire is accurate enough to be a threat, moreso than floundering smaller rounds that can't hardly hit the general vicinity. The squad can at least hit the general area enough to pin down even hardened enemies, this might not be true for the smaller cartridge.
Elite and high end soldiers can use this to extreme effect. A whole squad of battle rifles engaging a carbine equipped enemy at 600 yards puts the battle rifles at one hell of an advantage, they can direct fire halfways accurate enough to pin the enemy that can't truly respond in kind nearly as well. The battle rifles will be more likely to cause casualties with their general en mass fire at that range, can take better shots if they can get the upper hand in firepower suppression, help attack the enemey and force him out, surround him, or best yet, hold the advantage in fire till you wipe him down with big gun fire.
You end up with situations where machine guns and DMR's are effective enough to have the kinds of fire that can respond in kind enough to keep the enemy from gaining this edge. One or two guys with battle rifles/DMR's can put some parity back into the fight, the machine guns are the only other thing that can help keep long range use of en masse infantry fire from becoming an unwanted enemy advantage.