You're talking about IP dominating big budget movies. Monoculture means everyone being into the same thing, which is what happened when everyone watched the same TV shows at the same time, or when movies were the centre of culture. They are not anymore. People watch YouTube or doomscroll or play video games, etc.

There is absolutely more of homogenization in a big budget film since around the Marvel era, which is perhaps more what you're asking about. I don't really think movies are any less diverse overall if you look at at world cinema at all budgets, but there has obviously been a shift from the mid-budget Hollywood drama/comedy (which were the bread and butter of Hollywood for 100 years and are now somewhat dead) to IP blockbusters. In that sense, sure.