Between the ages of 3 and 5 children are still constructing their world view and are not always clear about which figures are fantasy and which reality. It’s not as clear cut as the old-fashioned view that they mis-attribute reality to fantasy figures, but there is definitely some confusion in their minds, particularly with figures which “look” real eg Santa or Superheroes portrayed by actors.
So at this developmental stage you are exposing your toddler to images of frequent graphic unpleasant violence between characters whose fantasy nature may not be entirely clear in her mind, and the concept that this violence is a perfectly normal, indeed expected, way to resolve conflict. This is very different than say a 9 or 10 year old who will be extremely clear that this is fantasy violence between made-up characters and bears no relation to the real world.
Do what you like with your own child - sounds like you are going to anyway. But I would think you foolish and irresponsible to take a child that age to see a movie like this.