He’s A Natural Leader
In Justice League, we’re set to see a different version of Batman – one who actually plays well with others. Most interpretations of the character will have you believe that he works better alone. Maybe in the past it’s been true, but Batfleck has had at least two Robins in the DCEU so far, thereby proving he’s not averse to having a partner to team up with in this new modern-day universe.
From all the stills and footage, we can see that Affleck will assume a strong leadership role of the League. Whether he’s actually made the official leader or not (our bet is that Supes will assume the mantle at the end of the film), he has the presence and clout to inspire and lead a group of new heroes into battle.
As the oldest of the bunch, it’s also likely that Batman will assume a mentorship role to Barry Allen/The Flash and possibly Vic Stone/Cyborg. From what we’ve seen, there’s certainly a strong bond between Bruce and Barry in the trailers.