I'm relatively new at this, so my focus is still theatrical, rather than cinematic. Thirteen out of seventeen plays I've written started with a wotif, a dramatic situation, which the main character then epitomized in some way. I then added characters who created the most conflict via contrasting personalities. One exception: an actress asked me to write a play featuring a mature actress. Three other plays were either built around character(s) or the wotif implied the MC so strongly, it's impossible to say which was the primary element for the script. Of my four screenplays under development, only one is based on character(s).

As I say, Jeff, every writer is different, every story is different. In one of the screenwriting roundtables I've done featuring a recurring group of about 6 or 7 writers, F. Scott Frazier said his process for developing and writing stories changes with each one. He doesn't have a set process. So the approach can vary WITHIN the lifespan of an individual writer. And as you suggest, that extends to how we come up with story concept, then go about prepping them. I suppose we can look at the organic nature of story as a built-in antidote against formulas and formulaic writing.