You can't judge the casting until you see their performances man.
People didn't like the idea of Robert Downey being Tony Stark, but once everyone saw his performance we saw what genius casting it was. Similarly Ryan Reynolds seemed like decent casting for GL, but it turned out he wasn't really the best casting choice for that role at all (too much of the Reynolds funny man routine in an unfunny script).
I will say though Henry Caville was good casting. But again I can only say that after seeing him perform in the role.
Downey was great casting. I don't know why people were complaining. Same with Hugh Jackman. When I look at those people, I can see their character. That's all I'm going on, not performance. Same with Margot Robbie and Ben Afleck.
Well you can't completely blame the director, because Val Kilmer was a much better Batman under the same director.
Sometimes big names with talent just don't suit a particular role, or simply don't "get" the role they're playing.
That's why genius casting can only be determined by the performance an actor gives in that particular role. Hence it being worrying that Ezra Miller didn't audition (I don't know that for sure, just repeating what someone else said on this thread).
Warner Brothers is to blame (yes, ad nauseum but it's true) for Batman Forever and Batman & Robin. They instructed Joel Schumacher to make those movies as campy as possible to sell more toys. He later apologized for making Batman & Robin on the movie's video commentary.
Clooney did suck as Batman and Kilmer was a lot better, but I wouldn't blame him for phoning it in when WB was only interested in advertising toys. Batman & Robin was a special case of bad and it didn't allow any actor or actress to display their talents.
That's what I'm kinda saying, though. Sometimes it's not the actors fault. If Clooney had free reign to do what he wanted, he could have been better. Haven't seen the movies in a while, so I'll take your word for it.
Unfortunately, it seems Lord and Miller won't be directing this as they have been officially announced to be the directors of a Han Solo spin off film set to be released in 2018. Great news for SW fans though!
Hopefully, they can get someone like Edgar Wright to fill in.