All movies operate on conveniace to one degree or another. Isn't it lucky that there was a garbage chute right next to Han and Leia when they needed it? That the Death Star II could fit the Falcon in it's trenches? That a mind controlled Selvig built a fail safe? That all the (organic) aliens shut down when Stark blows up the ship?
Then - again - make that part of the story. Have him away from Gotham during peace time undergoing training, but eventually a new Ra's/Joker/Bane like villain comes and start causing trouble, more than the resurgent citizens and police can handle. Blake, against his kung-fu mentors wishes, goes back. He goes back, does a lot of good...but not against the big fish. He's still just doesn't have 'it'. Even Gordon says so! He comes to Wayne Manor, tells Blake he knows he's the new Batman (because who else would it be?) and to stop. He's just not Bruce. Eventually, through persistence, extra training, something unique to Blake 'making the role his own' he overcomes all those obstacles, as all heroes do (including Bruce).
It works fine. But again... For a comic. Not for the movies... Reboot with Bruce.