Mxy, there are loads of movies out there with characters nobody has heard of before they go to watch it, and they are still huge sucesses. Nobody, or at least barely anybody had heard of Indiana Jones, Star Wars, Robocop or 1000s of other characters in movies, but they still went to see them because of good promotion of those films, and by your reckoning, word of mouth!
Lets face it, who the fuck knew Blade was even a Marvel comics character, but that didnt stop that film being a sucess!
But none of those ideas were directly attached to pre-existing concepts.
While JLA is a pre-existing concept, probably 80% of the worlds population has never heard of them, or knows who they are. A good enought marketing campaign will sell that movie to them based purely on special effects and action.
It also proves that people do not need to know who a character is for them to go see a movie!
