In fairness, I think DGG's HALLOWEEN trilogy is -- at very worst -- just a mixed bag (one pretty good movie, one not very good movie, one movie of debatable merit!). HALLOWEEN '18 should indicate he can put together a respectful continuation of a classic.
But the thing about THE EXORCIST, in particular, is that it's such a unique marriage of director (William Friedkin) and writer/producer (William Peter Blatty). You don't need both of them involved (THE EXORCIST III is only Blatty, and it's great), but I think you certainly need one of their voices... and neither of them are involved in the new movie (Blatty has passed and Friedkin has declined involvement in any other EXORCIST movies on general principle).