...ce League. Regardless of whether or not he was, in fact, a founding member in previous timelines, history, or eras, there can be nobody BUT Batman and Superman who usher in the Justice League on film. They are, after all, the first 2 comic book characters in history. And they are the biggest moneymakers for DC comics. It would be illogical and just bad for business if anyone else was to establish a JL continuity. The same argument could be made for WW and the rest of the original 7 but if you have to introduce the JL with a minority of membership, you'd be CRAZY not to have Batman and Superman as part of that minority.