There is no where to move it. 2019 is packed as well, especially when it comes to superhero films. Looking at the December releases, Aquaman, Bumblebee, and Mary Poppins are probably going to eat into eaxh others grosses, at least opening weekend wise, but they should be able to coexist, seeing as how Jumanji and The Last Jedi coexisted. Quality will determine the outcome imo.
Edit: Justice League outgrossed the last Transformers movie and DC films have a track record of opening upwards of 100 million for the past 10 years (sans JL and GL)
Aquaman, Shazam and Wonder Woman 84 are all confirmed and happening. After that is apparently Harley Quinn & The Birds of Prey (filming in January, likely releasing 3 months after WW84). After that is anyone's guess. Maybe it'll be Batman, maybe it'll be Suicide Squad 2. I doubt it'll be GLC or MOS2 though since neither has a director.