From the Avengers ∞ Spoiler thread...

RE: MCU vs DCU

I think that DC could compete with Marvel at the box office if there films were good enough. Wonder Woman demonstrated this last year, being released just a month before Spider-Dude: School Disco and still managing to become the 10th highest grossing film of that year, just behind Thur: Battle Royale.

And in 2008 Dark Knight was the #1 highest grossing film, totally outperforming Marvel's Iron Man and Universal/Marvel's Incredible Hulk. And although the first Avengers movie was #1 in 2012, The Dark Knight rises came in at a respectable 3rd place in box office sales. In 2013 Man of Steel still came in 9th place, one spot above Thor The Dark World (Iron Man 3 was #2).

BvS still came in #7 in 2016's sales, although much of that was just from the opening weekend and the film experienced a massive slump after that. Justice League didn't even make it to the Top 10 and the studio is estimated to have made a loss of up to US$100M. But that's not to say that DC's movies are unsalvageable. Universal's Hulk in 2003 only made a modest earning but they still persisted to make Incredible Hulk in 2008 (albeit in collaboration with Marvel Studios) which then became the launching pad for the current MCU.

There are 2 things that DC can do:
1/ Make stand-alone super hero/heroine movies that focus on singular character development of the main protagonist. This worked for the Nolan Batman Trilogy and Wonder Woman, and even Man of Steel to a lesser extent.
2/ Make another Justice League movie but make it fun and exciting. Ensemble cast movies will never be as character-driven as stand alone movies due to the nature of the beast, but you can still just make them fun and entertaining films.

And there's no reason why they can't do both. This is what Marvel's been doing for the past 10 years. Stand alone movies like Iron Man, Thor, Captain America, Black Panther, Dr. Strange, Ant-Man etc. as well as team-up movies like the Avengers. And they need to look at what makes Marvel's movies more interesting than their own. Basically DCU's failings comes from not understanding one of the key principles of the Art of War -- know your enemy^business rival.

P.S.: Another option may be if you can't beat them join them. Contact Disney/Marvel and see if they can work out a deal for a joint Avengers/Justice League team up movie. Let the MCU guys take the wheel and just sit back and watch the money flow in.