This is my problem with the complaints from DC fans. Casual fans of movies aren't wrapped up in this DC/Marvel beef. They also have been known to ignore critics if they like a movie. So ultimately, box office and DVD sales will tell you whether the critics have an agenda against DC. Casual fans generally did not enjoy Man of Steel and gave BvS mixed reviews. You can't claim that the entire world is in on this mass conspiracy, something is just not working, and it would be more advantageous to just listen to what people are saying about the film instead of crying about conspiracies.
And it's the casual fans that make up most of the viewers. I though Jurassic World was overrated but casual fans enjoyed it.
Marvel doesn't do much tinkering. They have a formula and stick with it. They have a good mix of catering to comic book heads while still making movies that will appeal to the rest of movie goers.
But as I said before the execs at DC and the people they hire to direct these movies keep creating stories and narratives they think are good instead of making movies most people will watch.
And another thing. One of the reasons why the MCU has been so successful is because the movies and actors are not polarizing. When you have so many characters in one universe that's important. Any time a character or movie overshadows the collective universe there it causes a distraction.
MOS is a prime example. It became so polarizing that it affected the production of BvS. BvS became so polarizing that it bled over into the production of SS.
Iron Man 3 was meh but it had not effect on the winter soldier. Age of Ultron was good not great but it had zero effect on the making of Ant Man.