David Zaslav had been chief executive of Warner Bros. Discovery for all of a few hours when he learned he had a problem.On April 11, the day his newly merged company began trading on Nasdaq, Mr. Zaslav greeted New York employees with pasta and ice cream bars, delivering an impromptu rallying cry to his new charges. He was on his way to Washington, next stop on the coronation tour, when a call came in.His team had just gotten its first look at data from CNN+, the much-promoted subscription streaming service started two weeks before, and the news was grim. Fewer than 10,000 viewers were watching at any given time, despite a multimillion dollar ad campaign and big hires like Chris Wallace. They were recommending a cold-eyed review.Three days later, shortly after Mr. Zaslav appeared with Oprah …
