At indoor distances, indexing only the front sight on a target will get perfectly acceptable hits for most people. At one time this was taught pretty commonly, but I assume that since optics became so commonplace it stopped being relevant. It works especially well in very dark rooms with a weaponlight. And it even takes a bit of the holdover issue out of the equation!
But, as you point out, the RDS is also fine for even the most astigmatized at those distances, so it works just as well. I suppose one might argue that if I can't use the optic at distance, and there's a trick to using irons at close range, why spend the money and add the weight of the optic?