I've never had a problem with the pacing, but director Renny Harlin said that when he made the prequel Exorcist: The Beginning he thought that the original was probably too slow for contemporary audiences because of the influence of MTV and commercials, and made a movie that was more appropriate for the youth of today; which IMHO is one of the worst movies ever made. Also, it was only made after they temporarily shelved the first version of the movie, made with a different script and director, because it didn't have enough puking and cussing. That version Exorcist: The Beginning, isn't great but it's okay.
Laughably, the Renny Harlin version makes a point of explaining how someone could be both a priest and an archeologist, as if they expect the audience to be confused by that. And the movie only makes sense if you don't know what either a priest or an archeologist actually does.
According to that movie, when Satan was cast out of heaven he landed in Kenya.