The strength of Ross' approach is that most of us grew up wondering what superheroes would look like in real life and his paintings get us as close as we're likely to get. But if you're going to ask, "what would this character look like in the real world" then you have to be ready when the answer is, "stupid."
Superman comes off fairly well, but for my money, Ross' Flash looks ridiculous, with that shiny suit and a seam right down the center of his cowl. Hal Jordan, whose Gil Kane-designed costumed always seemed so classy to me, looks like a reject from a ballet company when drawn "realistically." So many of these great, body-hugging outfits are revealed as goofy leotards when rendered by Ross. Which isn't so much a criticism of his abilities as his outlook. Sometimes the only thing separating "fun" from "stupid" is that well-crafted sense of UNreality, the ability of pencillers and inkers to take us up to the edge of reality but never over it. Even Neal Adams, who pioneered "realism" in comics (and in retrospect opened a Pandora's Box) actually created a sort of alternate reality, a world where everything looked accurate and tangible, but just slightly better than real. To me, comics offer something bigger, flashier and more exciting than reality and in the end, making superheroes "real," whether in story or art, is a comedown, a waste of potential.
The older-looking characters (and I love those Doc Savage covers) give the characters a gravitas and experience that seems apt for what he is trying to do (although the premises of Earth X and Kingdom Come lent themselves to that look). Ironically, portraying these characters as ancient probably has a negative effect on younger audiences in terms of reader identification and marketability.
I have a soft spot for those old Bama Doc covers, too, since they got me into Doc's world and by extension the world of pulps in general. Like Ross, Bama worked with models, and if anyone ever looked like a real life superhero it was Doc model (and former Flash Gordon) Steve Holland. But in retrospect, he really was too old to be the Doc in the stories (a "kid brother" to the Fantastic Five) and I have to wonder why Bama didn't just "leave out" a few facial crags and wrinkles.
KC Superman and Earth X Cap were fine with me, they were supposed to look older. But "Peace on Earth" Superman should have looked a lot younger. I'm as much a fan of "mature" heroes as anyone (to this day I think Chris Reeve looked too young for Superman, and Brandon Routh is a baby!), but there's a difference between grown-up and worn-out.
As far as posing, Ross' Supes isn't so bad, as a real-life Superman could afford to stand still and let the world throw things at him. But his Batman looks too beefy to raise his leg high enough to climb into the Batmobile, let alone kick a bad guy in the head.