You're right, players are bigger, faster, and stronger now: ALL players, meaning not only the defensive players chasing RBs, but the RBs themselves.
Put Jim Brown in Barry Sanders' era, and he is trained the same way Barry Sanders is. Considering how Jim Brown dominated his era (more than any RB has dominated ANY era), just imagine what he'd do in current times. The guy was able to rush for over 1,800 yards in 1963, w/ the training available to him @ the time. You think there's a chance that he could improve on that w/ the advancements made since then?
I don't "hate" on posts, I just have respect for the game, meaning not just the guys I see on TV, but those who paved their way.