Hollywood was on strike when Mark Ruffalo and Matt Stoller met over Zoom one day in 2023. But the movie star and the head of the American Economic Liberties Project had something bigger on their minds: the perils of huge Hollywood mergers. “We came together because we recognized the root cause of the [Writers Guild] strike,” Ruffalo and Stoller wrote in a New York Times op-ed published May 7. “A handful of corporations were swallowing an entir…