I hear where you are coming from and agree to a certain extent (though I would consider Man of Steel the first “modern” DC movie as it’s the first in the expanded universe). I know a lot of people like to cite the weekend drop off, but never mention that the Sunday following the premiere was Easter, so no surprise there.
I’m not trying to really defend the movie. Some will like it, some will hate it and some will say “meh.” In the end, I’d just rather see lines like “BvS was a critical failure. The movie made a monstrous amount of money (way less than Furious 7 or Jurassic World, though)” replaced with something like “despite being a critical failure, BvS finished 2016 with the seventh highest box office worldwide .” Hit it where it deserves it, but give credit where it’s due.