Given that Christian Bale’s first Batman performance was in 2005’s Batman Begins, presumably Armie Hammer was thinking back to what Bale did with the character in 2008’s The Dark Knight and 2012’s The Dark Knight Rises.
Since Hammer was still early into his acting career when Justice League: Mortal fell his way, it sounds like his Batman wasn’t closed to maturing into a veteran vigilante.
Regardless, Armie Hammer’s description from MTV’s Happy Sad Confused podcast of what Justice League: Mortal’s Batman would have been like lines up with most modern depictions of Bruce Wayne.
Having said that, Hammer also paints a picture of a Batman who’s way more unstable than we’re used to seeing, and thus wouldn’t be much of a team player when starting to work with the other Justice Leaguers.