I saw this film being a big potential disaster from the beginning because you could just see how rushed everything looked in trying to get this team thing going before we could firmly establish these new iterations of the cinematic universe characters.
I hate to do the marvel comparison, but we're talking hero teams, so it's relevant discussion.... If they made an Iron Man movie and then went into The Avengers it would not have been a good experience with me. It would have been too many characters all at once and so shallowly developed to the point if one of the heroes died I really wouldn't have cared. Having seen individual character developments through multiple films separate from the team, THAT is what made the team film stronger for me because I got a chance to get to know each character better than just throwing them all in one place for 2 hours and expecting people to just love it.
Was Avengers the best film? No not the best, but I really enjoyed seeing this journey from one hero to many through solo Avenger films that lead up to it. The pacing was good.
I REALLY would have loved to see a NEW Batman Film first, Wonder Woman, Flash (etc) and then bringing them together where it would have felt like a union of friends we've gotten a chance to know to work together in achieving victory over a massive evil force. BvS was just so weak in that area and it was a poorly executed film to launch Justice League, especially for those who aren't avid comic book readers. You have to connect with the audience and not just the hardcore people who know what's going on behind the scenes of all this. I was just such bad storytelling and character development.
The last time I saw this big drop thing that I can remember was when everyone went out to go see Batman and Robin, made that big opening weekend and then vanished off the face of the Earth because word got around fast that it sucked and people were done with it.