Aside from featuring the main conflict between Batman and Superman, it also had to deal with the aftermath of Man of Steel, introduce Wonder Woman, show other metahumans to tease Justice League and more.
Maybe if Boseman checked out that cut, he might have a different opinion.
It is true that the movie had a lot of balls to juggle, as it was laying groundwork for a lot of future DCEU projects.
There was so much material that the “Ultimate Edition” was released on home media, giving fans 30 extra minutes of story they didn’t see in theaters.