Which characters do you think would be difficult to work as a standalone hero with no connection to a greater shared universe? A lot of DC heroes weren't created with a shared universe in mind so sometimes it feels like certain parts of the universe don't fit. This doesn't apply to Robin or any of the side kicks, Robin would still work perfectly fine in a universe where Batman is the only hero with no Superman, Wonder Woman or the JL in sight. But the Teen Titans? Yes, that whole concept depends on their being other heroes with their own side kicks. Even if you focus on the Titans who aren't side kicks like Cyborg, Starfire and Raven, it still feels like there is something missing. Booster Gold would be another one. His whole premise involves stealing artifacts from a museum to go back to a time where heroes existed so he could become famous himself. You need the existence of other heroes to make him work. The Legion is an odd case because they are also heroes inspired by superheroes of the past but they are also a subset of the Superman franchise and thus primarily inspired by him. They could work if Superman is the only hero in the world but in a shared universe, it's weird that Superman would be the only one to have a legacy lasting up to the 31st century and everyone else is forgotten. Zatanna would be another odd case but that's largely because 97% of her appearances are as a guest star in someone else's story. Would she work as a stand alone if she had a longer run as a solo hero? There is also the Flashes. Would Wally work if he didn't have his Titans history and Barry was the sole hero he had in his life? Would Barry work as a character if he had never interacted with Hal, Ollie and the rest of the League? Can the Atom exist as a standalone hero in his world?