American Ballet Theatre is rich in talent. But does director Kevin McKenzie use the talent effectively? “Is he too evenhanded? In an effort to appease honored veterans and flatter new additions and encourage promising youngsters, does he spread the casting of major roles too thin, in a way that shortchanges the public? Wouldn’t coherent, recurrent casts, as has become the practice among singers recently at the Metropolitan Opera, mean more integrated, better rehearsed performances? And wouldn’t fewer principals in leading roles help build star images and thereby augment the box office?”