I haven't seen Birdman, but agree that all the 'oh no all the superhero movies what about Real Cinema' stuff is a bit weird. Literature, broadly defined, hasn't exactly shied away from fantastic tales throughout the ages.
I don't know about the mechanics of acting in one of these movies. Maybe all the stunt doubles and effects and green screen acting makes it a bit less fun. But who wouldn't want to play a wizard or a guy who can fly?
And the great thing about the contemporary age is that actors are much less likely to get stuck in those roles. Star Trek actors had a hard time finding more work. Christopher Reeve didn't have a great post-Superman career. Harrison Ford managed to break out of it, but that was kind of surprising at the time. Now you can play Gandalf and Magneto and still go on to do other things.
