People who do scientific studies of this (armies) have absolutely unequivocally found that optics improve speed and accuracy. The result of the ACR program in the 80s was that no rifle or ammo improved performance enough to be worth it, but optics were a total game changer. After this we got the flat top M16/M4 variants, and the M69 RCO (the Aimpoint Comp) and the ACOG on, pretty quickly, most every gun.
The same has been found, more anecdotally and individually, for a lot of people who shoot for themselves. RDS are they are the absolute go-to for all sorts of competition, as well as tactical work. Much much faster, more accurate, and other useful things like the dot floating in space so you can see the whole target, instead of having the gun obscuring much of it.
RDS on carbines should not be much or any higher than the iron sights. "Co-witness" is a common term, originally to mean you literally have to look through the iron sights, but now those are flip up or not present, so it's just used in the same plane as where the sights would be. This mechanical offset is only a problem at quite close ranges, but is easily accounted for; hostage rescue teams have always practiced their offset and can hit accurately enough to miss hostages with them. I am not tier 1 SF quality even on my best days and can easily account for offset at close ranges .
In practice, soldiers in the field rarely dialed range on their rifles, and range estimation is fraught with error so it's not super beneficial. Unless on a line with officers saying what range and when to fire, range dials are not super practical. So despite there being a handful of range-adjusting bases, they have all gone by the wayside, and holdovers are used. 5.56 is also fairly flat shooting, so the big orgs like armies that use it have no issues to their declared effective ranges aiming dead on. Further out, you can do well if you know holdover and watch for splash.