Wrong - and not bothering to see it is your loss.
Justice League will do very very well, even after the backlash of BvS. Can you remember the backlash from Man Of Steel?. In my total honest opinion i thought BvS was better than Age Of Ultron. Ultron was weak with plot holes and over crowding throughout and yet the critics hanged out of its ass.
BvS may have made $424m worldwide in 3.5 days, but it's only massive drop-offs from here unfortunately. Keep in mind that it has opened in every single country in the world (those that have theater chains & allow Hollywood movies, at least) Its domestic OW is a bit lower than Iron Man 3's, which indicates that this will almost surely fail to crack the $400m threshold. The domestic market is still the most important, since Hollywood studios don't get nearly as high a percentage of the total gross from international territories as they do from domestic revenues. The Chinese market (the world's 2nd most important by far) was not too enthralled by BvS. Experts say that the total in that market will be around $100m, an extremely negative result (Age Of Ultron made $240m in China) Most other international markets tend to burn out pretty quickly (even faster than North America)
I am not sure whether BvS will reach the $1B worldwide that is its minimum requirement. On top of that you have a generally negative reception.
I wanted this movie to succeed very badly, but the more I think of it, it was always a very tall order. The DC universe is really difficult to put on screen. Most of the characters have God-like powers and properties and this is a massive challenge for cinematic interpretations. Zack Snyder was given more than he could handle, in my opinion.
If you look at the MCU, they had the luxury of building their cinematic universe very gradually. They started with the one character that was the easiest to put on screen. Iron Man is just another, more cheerful version of Batman. No superpowers, a billionaire who derives his hero-status from a high-tech exoskeleton. The entire MCU was built around the relatively realistic character of Iron Man. He is a character that is only an exaggeration of reality, he basically is the idealized and glorified embodiment of the US Air Force and US capitalism. Remember that with the MCU, the Hulk movie was a relative failure, while Thor and Captain America where merely hits, barely making some money back. Iron Man almost single-handedly carried the entire thing forward until the first Avengers movie in which all of the characters came together.
It's difficult to tell whether the DCU should have gone down the same patient path. Maybe it would have been the better option. Maybe they should have just stuck to their guns with a Man of Steel 2 that introduces Batman, or a Batman standalone that introduces Wonder Woman, with Superman kept in the background. Dawn of Justice was a rushed effort to cram way too much in a single movie. Keep also in mind, that most moviegoers are not really that knowledgeable about comic books (I am sure that the vast majority of people did not get the Darkseid teasing etc)
In my opinion, the DCU should have used its most famous and bankable character and build from there, Batman. On the other hand, the recency effect from the Nolan movies discouraged WB from doing that. Man of Steel came only 10 months after The Dark Knight Rises. Warner Bros found themselves in a very tight spot. The MCU was marching forward relentlessly, the Nolan Bat-flicks were extremely recent, and they wanted to get going. It was an impossible task.
Warner Bros and DC need to calculate their next moves very carefully.