It really is an amazing thing that the DCEU was founded on the idea of being this grand multi-movie arc for Superman that got high-jacked by Batman....yet, as of now, the most successful characters to have emerged from it are Wonder Woman and Aquaman--two characters they had no long-term plans for and in fact intended to have killed in the Justice League sequel until Flash time traveled them back.
I said this in another forum, but the lessons to be learned from all this:
1) don't rush your shared universe
2) be willing to adjust the story based on audience response
and
3) stop assuming Batman and Superman (mostly Batman) are the only characters who matter