The major trend in this period was the Turks moving in, overwhelming the Arab Muslims and threatening the Byzantines.
The Turks adopted Islam, but they were Turks first and foremost, rather than Muslims. The religious angle was secondary to the ethnic.
Not to say the book isn't good, just that it may not reflect the most important factor (IMO!).
My rule of thumb is that anything written after 1950 is highly suspect.
IMO the best writer on these matters for decades now has been Jimmy Reston. His research is unmatched.
Thanks again. D-man