After how heart breaking BvS was, they need to go either one of two ways with Justice League.
Get an amazing script, and let Snyder handle the visuals. Or, have almost no story ala Fury Road, and just let Snyder go nuts with the visuals and action.
I still put the blame on WB for BvS. My gut says all they did was see dailies, saw how awesome it looked, and figured the final product would deliver.
No doubt they had the same facial expression that the producer of phantom menace did when he first saw it.