Daredevil had a bad director and script, treatment was bad and his acting back then too. Jensen would have been a really bad Batman, he can't act. Affleck in the past few years has grown as an actor - The Town, To The Wonder, The Company Of Men, Argo.
Think about it this way - everyone loves the first Batman movie, which means they were OK with Batman. Keaton was a comedian and he had 2/3 critically acclaimed good roles right before Batman happened to him. He doesn't even look like Bruce Wayne, yet the movie as a whole worked. Keaton would not be a good Batman in Val Kilmer's version of the script or Nolan's version of the script.
Right now my biggest concern isn't the actor as much it is who's making it and what the script is going to be, how it's all handled. Goyer and Snyder are meh. Their script may need a guy like Affleck to play their vision of Batman.