Sydney Sweeney being in Immaculate absolutely got way more people to see it. No doubt that "the movie star" is different and much less important today but people like Sweeney, Zendaya and Timothee Chalamet are undeniably pulling a younger crowd into movies that they wouldn't have otherwise watched.
Two big differences in Coppola's favor are that the internet seems to be with him & the movie and there's only one movie. Having the press largely on their side is a big plus that Horizon doesn't have and if Megalopolis doesn't do well, it's one high profile financial failure and it's done which...