Really? Tony Stark the domineering, amoral alcoholic? Peter Parker, the perpetually depressed, simpering ****weed who only becomes a hero because of what someone else thought he should do, and because of a situation that baldfaced self-interestedness created for him? Hank Pym, wife beater extraordinaire? Yeah, you're right, Marvel is the creator of the modern superhero. That's the problem.
No, the problem is keeping these guys is the same serial for decades.
Tony didn't start out as an alcaholic. The movie pretty much summed up why he's a great hero with his background. They even made the recent trend of changing the original use of a secret identity.
Peter Parker is supposed to be the working class superhero. He fights crime to make up for a mistake that cost him the life of his Uncle Ben. But they've kept him young, made him single again, because they don't want him to move on and still be Spider-Man.
The modern superhero isn't someone who's just born into greatness, like the Greek heroes. Most of them aren't descended from privilege or destined to be great. That lack of ego, or the initial destruction of ego, is part of why they're modern. They fight in a world that is no longer black and white.