So the traveling Rockettes booted Boston Ballet from its traditional home for the Nutcracker. But maybe that isn’t so bad. “Bring on the Rockettes. Competition makes everyone stronger. If the ballet has to retool its show to draw audiences, isn’t it likely to make it fresher and better? Beyond that, having to go up against everything from the Rockettes to ”The Lion King” to a hundred local ”Christmas Carol” productions may force the Ballet to think more deeply, more precisely, more artistically about just what its mission is.”