So the point of a single person is to help guide and connect everything together. They don't need to be strict about it, but someone has to have the overall shape of the universe. Plus that's an easier task when the universe is just getting started.

For example Gunn wrote the Superman film, and at some point he decided to add the Green Lantern Guy Gardner to his film. Did he pick Guy because Lanterns had already called dibs on Hal and John? Did he originally pick Hal/John for his film, but Lanterns wanted Hal and John so he swapped in Guy? Now that Gunn is using Guy, how do you make a Lanterns show and not include Guy Gardner at some point?

To look across the aisle, look at the casting of the new Black Panther in the MCU. It's clear Kevin Feige and Ryan Coogler had already had conversations about Black Panther 3 and finding a new T’Challa. Feige was planning a search and Coogler just called him up and said nope, I found our guy. That's the same level of freedom being talked about here.

Usually the problem happens higher up. Jumping universes again look at Star Wars, specifically The Mandalorian and Grogu. Dave Filoni and Jon Favreau had a whole plan for their TV series, but then they were told to scrap it and make a movie instead. So the series gets a rushed ending and then the film, which is fine, comes out too late and a lukewarm response.

Finding that balance is key. The previous DCEU never found that balance and they never found a person to actually oversee. Syder was the closest but for a number of different reasons that didn't work.