A "character arc" represents the changes in the character in different parts of the story. That is, how the impact of story events brings about changes in the character.
A "character development" is a description of a character at a point in time. That's a helpful thing to have, all other things being equal. My big fear is "that much" character development (at one particular time) will fix the character in that time period, and inhibit changes (or at least the audience perception of those changes) during the course of the story.
So are readers/viwers more interested in "character development" (background details of a character), or "character arc" (how the character changes). Put another way, which do you prioritize if they come into conflict, and how do you reconcile the two?