It seems entirely feasible to me that it'll be part of Batman's arc in this film could be starting off as more extreme/cynical and ending up somewhere a little more balanced by the end, as a result of Superman's impact on him. I mean, to me that's the beauty of what you can do with movie adaptations when you're mixing up different pieces of source material. Things can be more fluid. Characters can grow and change. I'm sure Batman is going to have to go through some sort of arc in this movie before he's going to be capable of being a part of a team with superpowered beings.
I could be completely wrong and I'd happily admit that. But it just makes some level of sense to go with a slightly more extreme Batman to help play up the contrast between Bats and Supes in this movie. I mean, if there's any movie to do that in, it's this one.