What's a "real" actor? If you mean a more established actor that's fine, but a real actor is very ambiguous. As long as he is committed than it doesn't matter. Plus he has built a likability and familiarity with the public/fans. Not saying he will get the part because of this, but it can help. Take Hemsworth for example. After Star Trek he really got notice, and was just in it for 10 mins, but his character and the emotions he poured into the role paid off. That wasn't the only thing that got him the part in Thor and may not have had anything to do with it, but after Star Trek people began to take notice and because of that open doors to audition and put his name out there.
As far as Luke Cage goes, at this point, I don't care. I don't know enough about the character and given the climate of superhero movies and the direction filmmakers/studios are going I can see almost any black actor getting the role.
Oh and as far as having wrestlers play superheroes, I'm for it as long as they can act and play the role. The Rock as Teth Adam has my vote, and I think HHH would make a good THOR Sci-fi movie or something along the lines of Conan.