You think the Vikings, Bears, and Chiefs haven't gotten proper return on their investment? Murray has an inability to stay healthy, but that could've been with any player drafted at any position. Bell is currently a monster, and Shady will probably have 1,500 yards from scrimmage in a year when his line was decimated. He's pretty much a 1,600 scrimmage yards per season back aside from the years when he explodes for over 2,000. As for Lynch, he was a risk prior to draft, and the Bills were unable to contain that risk, unlike the team that traded for him. But he was a 1,300 yards from scrimmage back on a very bad team in Buffalo.
If you're going to judge proper return on investment in Superbowls, that's way too steep, and unrealistic. Only one of those trophies come out per season, and this is the ultimate team game. Which means you'll need more than just a star RB, or star QB to make it happen.