I know it's a common thing to have serious doubts about a casting decision when it comes to batman, but I think it's a mistake to write him off just yet. Yes he's known as the guy from twilight but he's moved on far from that now and has done a lot of indie stuff and worked closely with directors to develop his craft. He was great in The Rover and Good Time (plus for a British guy, he can do accents really well). As a younger Bruce Wayne, I think it's good casting personally.
Affleck was pretty good for the role, was a decent Bruce Wayne, he just lost his confidence in the role and those movies were a mess. He was ridiculed for Daredevil and that anxiety must have come back after BvS got crapped on. He was phoning it in in JL.