William McCants on ISIS

I am reading William McCants book on ISIS: The ISIS Apocalypse: The History, Strategy, and Doomsday Vision of the Islamic State.  There is no question that he knows his subject well and is steeped in the knowledge of Islam and its history but his approach is marred by this: 1) theologocentric cast: he takes at face value whatever Muslim organizations say and take that as the real motive and determinant.  This is like those Kremlinologist who assumed that Soviet policies stem only from Marxism-Leninism and nothing else.  2) He is too influenced by the approaches of Michael Cook and Patrician Crone. 3) while he is an interesting writer he sometimes tries too hard to appeal to American readers with sentences like this: (he is talking about the Mahdi, mind you): "Think Jesus and George Washington rolled into one" (I can't cite the page number because I am reading the electronic version of the book).