Agree 100% but Justice League was set up to fail.
You can't do a comic book team up movie where you are introducing multiple heroes as well as a villain. It just doesn't work. We'd never seen Aquaman, Flash, or Cyborg. People know who the flash is but Aquaman and especially Cyborg are entirely new characters to a lot of people.
When the first Avengers movie came out, We'd had two Iron Man movies, a Captain America movie, and a Thor movie. Black Widow was introduced in Iron Man 2, Hawkeye in Thor, and ostensibly the bad guy in Loki in Thor. We had seen every major player in the movie in a prior movie. Coming in cold and having to introduce all of those characters makes the movie be 3-4 hours to make any sense.
Those are really good points. It makes you wonder how JL would have fared had we already had Flash, Wonder Woman and Aquaman solo movies. They could have had end credit scenes with Batman sitting in the Flash's apartment, Bruce Wayne landing his private jet in Iceland, Batman looking at Hall of Justice blueprints, etc
They could have still introduced Cyborg (I dont think a Cyborg solo movie would have done well) and brought back Superman in JL, but it wouldn't have felt like such an exposition-fest had the other members already been in play.