As much as I like Boorman & thought he made the best of a bad situation, did no one remember the considerable on-screen chuckles generated by the sight of Sean Connery diapered up for the piculiar "Zardoz"? I wonder if the scope of the production of "Exorcist II" was just too much for a young director to bear, especially with a major studio calling many of the shots.
I wonder if Brian de Palma could have lent some of the crackling energy & garish carnage from the prom sequence of "Carrie" to the climactic moments of "The Heretic" or how his split screen techniques could have benefited the ridiculous sync machine. I wonder if a Scorsese could have lent dramatic weight to the relationships or if a Hitchcock could have trimmed "Exorcist II" down to the elements required to tell a meaningful story in a visually important way. What could Friedkin have made of it, for that matter.
Not knocking Boorman exactly but the best than can be said for the "Exorcist II" is that is a well designed, carefully crafted disaster. I look at the dedication of Richard Rush in getting "The Stunt Man" made and released his way and wonder if that's the kind of guts it would have taken to get "Exorxist II: The Heretic" done right.