Optics improve hit probability.
How much depends on the overall scenario. I'm not convinced that a red dot would improve hit probability for me inside my house, for example. I don't really need to use the sights at all.
WRT fast acquisition, red dots can really improve that, but so does training with irons. Combine the red dot and that training, and you can get the best performance.
It seems to me that many rifle shooters can't handle a long gun worth spit, though.
For the vast majority of the rest of us an optic, either reflex or magnified improves the utility of the firearm.
Accuracy, yes. Past a certain distance, a rifle can be almost wasted without magnification -- but don't tell that to the guys who can routinely hit a military target at 600 yards with A2 sights.
Utility is a conditional thing, though.
Size, weight, complexity, cost, maintenance, points of failure are all increased when you add an optic to the AR. Reliability in rough conditions is decreased.
By how much? Depends, of course.
Is the tradeoff worth it? Probably most of the time.
Still, "utility" is conditional. I find a stainless Ranch Rifle to have more utility than an AR, in some circumstances. It's much sleeker, easier to stash, lighter, and it points better.
Does that mean I'd rather use it in a match at 300 yards, or even 100? No.
"Utility" is a different thing.
Sometimes a heavy, bulky rifle that requires batteries that don't like cold weather, with glass that can break if you drop it on a rock, doesn't off the most
utility.
