I would argue that RPGs are built around increasing stats and the value of the character's equipment. With a die-hard realistic setting, you can only go so far because there simply are certain limits if you don't incorporate a) magic (fantasy) or b) high-tech (post-apoc/cyberpunk) into it.
In a "realistic" RPG, you could maybe make your character tougher and via physical training and stronger by giving him increasingly powerful weapons - guns, assault rifles, rocket launchers, whatnot - but at the end of the day, this would not suffice to explain how your fellow can survive against the increasingly nasty and numerous enemies the game throws at you.