"The movie does start with the correct choice of having King's famous line "The man in black fled across the desert and the gunslinger followed""

This is incorrect. The movie does not start with this line as it should have, the line is said in a later scene.

This is an important distinction because this line being in the movie is not what matters, what matters is that the line is the first line in the story.

You should definitely watch his Haunting of Hill House series on Netflix if you haven't already. He very much explores those themes in the series, even going so far as to have each sibling (from oldest to youngest) represent the stages of grief.