If that was true then titles like Magic of Shazam, Batman:BatB, DC Animated Adventures and Superman Family would be breaking sales records and dictating the tone of Super Hero comics.
The problem with those titles are that they aren't the mainstream
books, not the in-continuity
versions of the characters. People -- of ANY age -- want to know that what they're reading "counts", and those ancillary books don't. That's why those are always guaranteed to sell low. Moreover, such books are also part of the "secret clubhouse" mentality, isolating potential future supporters away from the mainstream books.
That's why I advocate making the in-continuity
titles for all-ages, so that no one is left out.
If Marvel and DC want to take a two tier approach to content, with one suitable for children and one suitable for mature audiences, more power to them. Your proposal to enforce teenagers to suffer through saccharine child's content is just as offensive as the people you decry for forcing Batman to have casual sex in his monthly comic and that's why it won't result in a net gain in expanded readership.
That isn't my proposal.
That's your ASSUMPTION.
And what happens when you "assume"??
The irony here is that WB Animation has been showing how to handle all-ages stories that even your "kids and adolescents" have enjoyed for decades now. Batman: The Animated Series, Superman: The Animated Series, Justice League, JLU, Static Shock... all featuring the EXACT SAME cast of characters that DC handles all the time, but DONE BETTER!
Your problem is that you automatically ASSUME that "All-ages" means "For babies!" As I've been saying, people from Disney and Pixar to WB Animation have been proving otherwise time and again for ages now; you are just one of the people who remain oblivious about it even as it keeps happening around you.